The best way to pick a color is to look at cars on the street and in lots. Once you start honing in on a color you like, try to see it in full sun and overcast conditions.
I saw a software like you mention at Summit Racing for choosing wheels. It actually had Firstgen birds that you could change colors, ride height and wheels on. I played with it for quite a while and found it moderately useful. Sorry, but I don't recall the name of it.
I would still look at other cars and form a picture in your mind of what you want.
