With something like a star you probably want to use intarsia. There is probably a video about that on this site, maybe under advanced techniques (don't let that scare you). Intarsia is easiest performed flat, working back and forth. You use a separate bit of yarn for each of the places, introducing them as you need to and working across one color to the use of the next one, dropping the first color and picking up the second one. Then you reverse the process on the way back. The main trick to be observed is to pick up the new color from under the old one at each change to kind of intertwine them, if you don't you will be knitting separate sections that are not connected at all, thereby making slits/holes all over the place.