They'll change color to green. They are called "Arus", which means they're strictly yellow as youngsters, then green with white, or blue markings when they're older...at least that's what my boyfriend says.
The big one is already starting to change...you can see it on her back in the first pic.
I haven't decided which is harder...fish or snakes. I haven't had my snakes long enough to know...but starting out, they're not nearly as complicated as SWF, that's for sure!