Our skin is our biggest organ, and it comes in many different colors. These different colors, referred to as skin tones, are determined by our outer layer's supply of a pigment called melanin. People with darker skin have more melanin than people with pale skin [source: National Geographic]. To understand why there are so many different skin colors, it's important to understand how melanin works.

Melanin serves as your body's defense against ultraviolet rays, more commonly referred to as UV rays. These rays are incredibly damaging and can ultimately cause skin cancer if you don't protect yourself. That's where melanin comes in. You know that your skin changes color when you stay in the sun too long. When UV rays start penetrating our bodies, skin cells called melanocytes kick into high gear and start producing melanin, which results in a tan. People with fair skin, however, tend to burn, because they have fewer melanocytes and, thus, produce less melanin. Extreme burns can lead to all kinds of unpleasantness, including infections and shock.

Some people just naturally have more melanin in their skin. They remain dark even in the absence of UV rays, and they don't burn as easily when they go out in the sun. Those whose families hail from Africa or India, for example, tend to have darker skin than European natives. Researchers believe this is the result of evolution: If you have dark skin, it's likely your ancestors once lived in tropical regions, where they were constantly bombarded with UV rays. Fair skin indicates you're a descendant of people who lived much farther from the equator.

Knowing your skin tone is important. Not only will you be able to better protect yourself from the sun's harmful rays and receive more accurate treatment for certain skin conditions, but you'll also be able to match clothing and hair color to better suit your body's biggest organ. It's not difficult to determine.

The simple distinction when referring to skin tone is warm or cool. To determine yours, simply look at your arm. What color are your veins? If they're blue, then you're a cool skin tone. If they're green, you've got yellow undertones, making you a warm skin tone. But, as you've probably noticed when make-up shopping or reading a fashion magazine, the descriptions and distinctions often go much deeper [source: CBS].

Read on to find out more about skin tones and where you fall on the spectrum.