It's pretty simple really. On one of the I'd tags on the bike there should be a code, they're usually found either on the neck or on the bottom of the bike on the frame rail. If you can't find it, look up the available colors for that year and make of your bike. Most are offered in only a couple different colors for any particular year, so it won't be too difficult to figure it out. Take that info and code to any automotive paint supply store and they should have books with color samples to compare and look the code up so you can see the paint.