I don't know which colors fetch the highest price but some of the rarer colors to be on the lookout for (if you can even find them) are: apricot, nutmeg, cinnamon and blue fawn. They would probably be the most sought after. Good luck!
Pastels sell very well as we'll as butterscotch. But in order to get these high prices for calls you have to have a name built up other wise don't look to get over $75 a pair out of them. They are one of the hardest breeds of poultry to hatch and raise as well. Your highest priced birds though are whites and grays... Top of the line birds I've seen go for up to $800 each