If your looking for more colour variation and dont have a sprayer.... Use EUROPEN GRAFFITI SPRAY BOMBS. Each of these companies have 140 or so colours, and the quality kicks the ass of anything made in North America and will be well worth the extra couple bucks.
1)do all the prep thats in the mentioned spray paint guide
2)paint surface with a spray paint formulated for plastic (like krylon fusion) as a primer. Select the colour nearest your final choice. Let dry completely.
3)skuff again and paint with Montana HARDCORE ( http://www.mtncolors.com/
) or Belton Molow premium ( http://www.artprimo.com/belton_molotow_spray_paint.php
). MAKE SURE YOU SHAKE THE CANS WAY MORE THAN RECCOMENDED. They've been sitting on a boat for a while.
4) clear coat (I like krylon for this)
If you live in a big enough city, chance are there is a local graffiti store, or HIP HOP store that stocks them. Choosing paint colours over the internet sucks for obvious reasons.