That's a family of morays. Blue, yellow and green sounds like a fimbriated moray to me.
Do you have a pic? What size tank are you planning? There are several different sizes of morays, some work in smaller tanks, some need large homes.
If you are gettings eels, you must check out Reef Fishes, Vol. One. It has photos, tank size, care level, hardiness, etc...great for quick research on morays.
I have three morays: a tesselata (gets huge), a blackedge or ocellated moray (gets fat, but stays around 2-2.5 feet) and a ghost moray (about 30" and thin as a magic marker).
On the whole, most morays are great tank pets...they are very hardy, can tolerate a lot of water and lighting conditions and very interesting to watch.
Please provide a few more details, and I'd be able to be more specific, as will the rest of us on this board.