When you open and fill up a food pen, each of your creatu automaticly takes one everyday. This raises thier hunger and keeps it up, as well as keeps them from dieing, It's a miricall when you can't get on Rescreatu for a while.
You change a pet's color by two ways: THe first is the natuaral color jelly bean. Feed it to the pet of your choice, and it will randomly change its color to any of the naturals. THis includes Natural, Sepia, Cream, Black, Silver, Blonde, and Albino.
For other colors, like Orchird, Indigo, Magenta, Gold/Silver, and a few others, you need to buy the die kits, or DKs, from the Black Market, if they're in stock.
Hope that helps.