Tetrachromy is found in women who have four cones instead of three. This mutation allows some women to see hundreds of millions of colors instead of just millions. Many of them are artists. It's a very rare mutation and is only found in women, most often runs in families where there is some degree of color blindness in a male relative.
http://en.m.wikipedia.org/wiki/Tetrachromacy

I have a male relative with some colorblindness, but am not an artist and don't think that I have any special color perceiving abilities.

Unfortunately, there is no online test to detect whether one is tetrachromic.. But one woman who is said that there is a certain online color gradation test that can give you an indication of how well you see colors.

I took this test and consistently score a zero. It made me wanted to get tested for tetrachromy. What do you score and are you an artist?

http://www.xrite.com/custom_page.aspx?pageid=77&lang=en