Just go in the paint shop and try every color you think might look good. But DON'T exit the paint shop when you're done. Use the PS button to quit the game. That way you don't lose the paint chips or money.
Then restart the game and paint it whatever color you picked, and you only lose that paint chip and $2000. The game REALLY should have a paint preview function...
or just a paintchip store where you can buy em in bulk
example regular paints 500 cr each
rare paints 3k cr each
I have mine in WRC Blue Mica, the Impreza paint, looks nice, dark grey rims.