Hello! Special traits are generally gained through trades (as a MYO slot in exchange for w/e) or already available on designs as you've said. :] I don't sell them outright because I want them to remain a bit more exclusive and unique than the others, since the possibilities cover "everything that isn't normally found on Dreamies" which is endless~ the sheet is just to give a feeler of mutations that happen.

For bald tails, you can choose any color really! In the past I had it that Dreamies' skin color beneath the fur was a duller and either lighter or darker shade than their base coat's color (so a red dreamy would have salmon or pink skin) and the blood was a more saturated color from their base coat as well. That's all been left out now because I want people to have fun with that sort of thing however they like, but if you did want any kind of basis, there's that. c: