The colored part of your eye is called the iris, and it's made up of two layers - the thin epithelium at the back and the stroma at the front. The stroma is made up of colorless collagen fibers, and your genetics for melanin (pigmentation in your skin and iris) is also what determines your eye color.
People with brown eyes, for example, have a high concentration of melanin in their stroma which typically means they have plenty of melanin in their skin, as well. They will typically tan rather than sunburn. Brown eyes are a dominant gene.
Green eyes or hazel eyes will have some melanin in their stroma, but not as much as brown eyes.
Blue eyes are potentially the most fascinating, as their color is entirely structural and this is a recessive gene. People with blue eyes have a completely colorless stroma with no pigment at all, which means that all the light that enters is scattered back. As a result of the Tyndall effect, this creates a blue hue, just like the sky. People with blue eyes have very little or no melanin in their skin and will have more issues with sunburn and a higher risk for melanoma. Blue eyes are very sensitive to sunlight and polarized Maui Jim sunglasses or photochromic lenses offer great comfort to these patients. Children with blue eyes should have transition lenses or sunglasses. Even wearing a cap or hat makes a huge difference in comfort. Macular degeneration seems more prevalent in lighter colored eyes.
My three kids all have blue eyes and they are constantly reminded about the dangers of sunburn and melanoma compared to their cousins with brown eyes. As the warmer seasons arrive, I wish all of you a safe summer.