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my dad and aunt are twins

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-https://www.thetech.org/ask-a-geneticist/ask126
-https://www.hudsonalpha.org/the-genetics-of-eye-color/
-https://medlineplus.gov/genetics/understanding/traits/eyecolor/#:~:text=Genes%20with%20reported%20roles%20in,eye%20colors%20in%20different%20people.
-https://topdoctormagazine.com/research/news/the-genetics-of-eye-color-are-more-complex-than-we-thought/
-https://www.news-medical.net/health/Genetics-of-Eye-Color.aspx
-https://www.thetech.org/ask-a-geneticist/ask59

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Editor's note (7/20/2021): Some information in this article is out of date. Scientists now know that eye color is a complex trait, influenced by at least 50 different genes.
The short answer is that we don't know. Unfortunately, very little work has been done on eye colors other than blue, green, and brown. For this answer, I'll focus on where hazel eyes might fit into the picture. Hopefully you'll get an idea of how quickly genetics can get too complicated to figure out easily.

So why don't we know more about the genetics of hazel eyes? Part of the reason comes from the difficulty of defining "hazel." In other words, when is hazel actually brown? Or green?

Another reason is that the inheritance is probably complicated, and not as "simple" as blue, green, and brown eyes.

So how might something like hazel eyes work? No one knows for sure, but I'll discuss some possibilities. But before that, it is important to go into more about eye color.

Brown, green and blue eye color comes from a pigment called melanin. Brown eyes have a lot of melanin in the iris, green eyes have a medium amount, and blue eyes have little or no pigment.

Two genes, BEY2 and GEY, work together to make brown, green, or blue eyes. Each gene comes in two versions or alleles.

One form of BEY2 makes lots of melanin (and is usually referred to as B) while the other form makes only a little ( b). One form of GEY makes some melanin ( G) while the other makes only a little ( b).

So how do you get eye color from all of this? If you have B you get brown eyes, G (but no B) you get green eyes and if you only have b, then you get blue eyes.

Most likely, hazel eyes simply have more melanin than green eyes but less than brown eyes. There are lots of ways to get this level of melanin genetically.

It may be that hazel eyes are the result of genes different from GEY and BEY2. Something like HEY for hazel. And maybe HEY is a bit like BEY2 and GEY in that it comes in two forms -- one that makes enough melanin for hazel eyes ( H) and one that makes little or no melanin ( b).

If this were true, the scheme for eye color would have to be changed. In the new scheme, you would have brown eyes if you had B, hazel eyes if you had H but not B, green eyes if you had G but not H or B and blue eyes if you only had b.

My gut tells me this probably isn't the answer. Even though this sounds pretty complex, it seems like it wouldn't be that much harder to tease out than green and brown eyes.

We still do not completely understand the genetics of eye color, particularly when it comes to less common colors, like hazel. (Image via Shutterstock)

Another possibility is a variation on this theme. Maybe hazel eyes come from different versions of BEY2 or GEY. I said at the outset that there were two versions of each gene. But what if there were more? What if there were many versions that result in the various shades of color we see?

This is certainly plausible and some recent research suggests that this might be part of the story. But again, we don't know. I would think the genetics again would be easy enough that it would have been figured out by now.

Another possibility is that there may be modifier genes. These are genes that would affect how much melanin BEY2 or GEY make. For example, you could get a gene that has GEY make more melanin or BEY2 make less. The end result would be hazel eyes.

What might this inheritance pattern look like? Pretty complicated.

Before launching into this, we need to remember one more thing. We have two copies of most of our genes -- one from mom and one from dad. What this means is that there are actually a number of ways of combining genes to end up with various eye colors.

For brown, green, and blue eyes, the possibilities using BEY2 and GEY are:

Now imagine a modifier gene that can give you hazel eyes by having GEY make more melanin. This gene comes in two flavors -- M increases the amount of melanin GEY makes and m has no effect. As you can see, it is possible to have brown eyes and have a B and a b version of the BEY2 gene. Or green eyes and have a G and a b version of GEY. These people are carriers for blue eyes.

OK, so to have hazel eyes you need a G from the GEY gene and an M from our modifier gene. M would not give hazel eyes with b. Why? Because b is really a broken version of G -- b makes so little melanin because it doesn't work. M can't fix a gene -- it can only affect how much melanin a working GEY gene makes.

So what are the genetic combinations that give various eye colors using M? To simplify things, we'll ignore BEY2 and just concentrate on green, blue, and hazel.

Now we're finally ready to look at some examples of how hazel eyes might be inherited. First, let's imagine a blue-eyed parent with bbmm and a hazel-eyed parent with GGMM.

The blue-eyed parent can only give bm to his children and the hazel-eyed parent can only give GM. So, all of their children will be GbMm or hazel-eyed carriers for green and blue eyes.

Let's look at a more interesting example: a blue-eyed parent, bbMM, and a green-eyed parent, GGmm.

This time, the blue-eyed parent can only give bM. The hazel-eyed parent can only give Gm. The end result is all GbMm or hazel eyes! A blue and a green-eyed parent will have all hazel-eyed kids.

This is one of the reasons I like the modifier gene explanation so much. It can help explain how green and blue-eyed parents might have hazel-eyed kids.

Finally, let's tackle a tough one. Imagine two hazel-eyed parents GbMm. What would their kids look like? For this, we need to bring out the old Punnett square.

The way a Punnett square works is you make a table. You put all the possible gene combinations for one parent on top, and all the gene combinations for the other parent on the side. For our example, you'd get something like this:

The next step is to match up squares. This will figure out all possible combinations and how likely they'll be.

From this the results are that there is a 4 in 16 chance for blue eyes, a 3 in 16 chance for green and a 9 in 16 chance for hazel. Even though this looks awful, it might be possible to figure things out if this were all that was involved.

Now imagine adding the brown gene to the mix. And another modifier that decreases melanin from BEY2 instead of increasing melanin from GEY. And now sprinkle in different modifier genes that increase or decrease melanin made by different amounts. And modifier genes that affect the modifier genes.

In reality, eye color may be a result of all of these ideas -- hazel eye color genes, modifier genes, and different versions of BEY2 and GEY! As you can see, it all gets complicated pretty quickly. We should be thankful that green, blue, and brown are as simple as they are.

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How do the genes for uncommon eye colors work?

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Editor's note (7/20/2021): Some information in this article is out of date. Scientists now know that eye color is a complex trait, influenced by at least 50 different genes. The short answer is that we don't know. Unfortunately, very little work has been done on eye colors other than blue, green, and brown.

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Unfortunately due to unexpected deaths I was not able to get photos for everyone in the family

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Looking at what I wrote, I made an error with my grandparents genotype. One grandparent could have homozygous BB, but very unlikely. 

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Determining the Genotypes of my Family P1

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Determining the Genotypes of my Family P1

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^With that being said this does not help determining F2 genotypes, since we know my uncle and mom would have to be Bb or there would be no hazel eyes in F2, only brown.
My Mom's Side
P
With my grandparents they have many genotype possibilities- BbGb,BbGG, and possible one grandparent can be Bbbb. And like I said above one grandparent could have BB homozygous but very unlikely considering a Dihybrid cross I have tried. Sadly I could not get enough information on my grandparents family (because they live out of country) to determine the exact genotype. However I do know that the green allele is in the family.
Moving on to my mom and uncle.
F1
This is where I had more trouble determining the exact genotype. Since brown is dominant there is no way of knowing whether the green allele is GG or Gb.
I since my cousins and I all have hazel eyes that BB homozygous is out of the question.
So the possibilities for both my mom and uncle are: BbGb or BbGG
F2
In conclusion
I believe my cousins and I have both possibilities of bbGb or bbGG.
The only way of knowing which genotype we have would be through the next generation
for example:
If I were to have a child with a blue eyed man, bbbb
and I had a blue eyed child, My genotype would be 100% -bbGb.
Unfortunately I did not come to a final genotype for my hazel eyes however it has been an eye opener to see how eye colour genetics works when looking at my family.

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What we know:
-one blue eyed child
Werner, blue eyes- bbbb
Valerie, blue eyes- therefore we know she has genotype of bbbb, since that is the only genotype to have blue eyes.
and their child Alicia also has bbbb

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What we know
-one blue eyed child
Steve, blue eyes- bbbb
Jody, brown eyes- Bbbb, BBbb, BbGb
- After looking at the work from Liesa and James, I already know the possibilities from BBbb with bbbb and that is not possible again for this case due to their child having blue eyes.
Therefore, I assume jody has Bbbb
Note: there is a possibility that jody could have BbGb however there is not enough information to know for sure. And the possibilities for blue eyes with BbGb would be 25% so it would be less likely.

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What we know:
-one blue eyed child
-one brown eyed child
Leisa, blue eyes- bbbb
James, brown eyes- Bbbb, BBbb, BbGb
-since one child blue eyes and the other is brown we know James genotype has to be Bbbb. Because if genotype was BBbb there would be 0% chance of having a blue eyed child. It is also possible for James to have BbGb, however there is not enough information to know for sure.
However after doing the DiHybrid cross the result of bbbb + Bbbb would seem to be correct based off of the information of the children's eyes.

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Determining the Genotypes of my Family P2

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Determining the Genotypes of my Family P2

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My Dad's side
P
Both Grandparents are blue eyed, therefore the only possible genotype for my grandparents is bbbb.
F1
Four children all blue eyes, therefore genotype for all of siblings is bbbb.
F2 and family's partners will be shown in the following >>>

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From research I've found it is hard to make out what genes give a person hazel eyes (typically hazel is a combination of brown, blue and green). However from what I have read, we can include hazel eyes into the green eye category. Since hazel does have a green involved within the eye colour and there are many more factors towards hazel eyes that are a little out of my range of knowledge from just research. From what I know melanin is what gives skin, hair and eyes their colour. Melanin is made from cells called melanocytes, where it is stored in melanosomes. But it all depends on the amount of melanin stored in each melanosome and the amount of melanosomes in each melanocyte. The amount of melanin total is what gives pigmentation. Therefore, more melanin=more pigmentation (brown eyes), less melanin=less pigmentation (blue eyes). And if someone were to have no melanin they would have the albinism gene mutation when they have no pigment to their skin, hair or eyes (typically they have very light blue eyes but in some cases a person can have red/pink eyes). Talking about genes, there are over 16 genes that effect eye colour (many of the genes are also involved with skin and hair colour). But today I am only going to work with 2 genes.
The two genes I worked with are:
Bey 2- known for coding brown (B) and blue (b) eye colour
Gey- known for coding blue (b) and green (G) eye colour
Dominant and Recessive Alleles
Within the Bey 2 gene
B- Brown Dominant
b- Blue recessive
Within the Gey gene
G- Green Dominant
b- Blue Recessive
Understanding the Genotypes
bbbb- is the only genotype to have blue eyes
bbGb or bbGG- result in green eyes
BbGG, BBGG, Bbbb, BBbb, BbGb, BBGb- all result to having brown eyes
however
BbGG, BbGb- would be carriers of the green eye allele and are able to have a green eye child if their partner is green or blue eyed.
Bbbb- carrier of blue eye gene and with a blue eyed partner it is possible to have a blue eyed child

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Growing up I was always the odd person out in my family when it came to eye colour. My mom's side have all brown eyes and my dad's side all have blue eyes. I was the first grand daughter in my family and I have hazel eyes. I was always so curious how I got this eye colour. Then my cousins on my mom's side were born, and they also have hazel eyes. So I was very intrigued on how we were the only ones with the hazel eye colour.

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Uncle Werner and Valerie

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Aunt Liesa and James

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Uncle Steve and cousin Jaxon

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bbbb, blue eyes

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bbbb, blue eyes

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Bbbb, brown eyes

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bbbb, blue eyes

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hazel eyes

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hazel eyes

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hazel eyes

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bbbb, blue eyes

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Bbbb, brown eyes

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Bbbb, brown eyes

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bbbb, blue eyes

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bbbb, blue eyes

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bbbb, blue eyes

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bbbb, blue eyes

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bbbb, blue eyes

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BbGb/BbGG, brown eyes

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BbGb/BbGG, brown eyes

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bbbb, blue eyes

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bbbb, blue eyes

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Bbbb/BbGb/BbGG, brown eyes

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Bbbb/BbGb/BbGG, brown eyes

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my grandma and grandpa

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Uncle's family