The colour wheel is made up of many colours, shades and even tone, all starting off of the primary colours of Red, Blue and Yellow. When I was in Makeup School my teacher made an excellent point of saying that realistically all you needed in your kit was these primary colours along with a white, and from these 3 colours and one tone you could create any colour. Good advice considering the cost you can rack up if you want your makeup bag or kit to provide alot of options, especially as a make up artist.
As complex as understanding colour may seem when looking at the colour wheel, its actually pretty easy. All you really have to remember is that the colour opposite the one you are trying to match is the best compliment to that colour. Here is the colour wheel, following the colour wheel is an example of this rule.
Using the colour wheel above, lets say you have blue eyes. look at the blue area of the wheel and then look at the colours displayed opposite of the blue. So your colour choice would be reds, oranges including varying shades like pinks and peach. Brown eyes have it the easiest, although brown eyes can wear any colour and shade, blues, greens and purples work the best to make a brown eye really pop. Although brown is not part of the colour wheel due to it being a compliment colour, it is a warm colour, therefore if it was going to be on the wheel it would be on the side of orange, yellow and even green, since many times the colour brown is made up of these colours.
No matter what the rules are, rules were made to be broken, and at the end of the day if you feel comfortable in it and love it, you can wear any colour you want, regardless of how they are decorated, eyes are the window to the soul, so whether bare or coloured they are always beautiful.