Here's a pic of their backs; its overcast outside right now so its again a bit of a dark pic. Basically, they have these big, chunky scales on their backs, so I found an old reference photo of a pair of crocodiles (eating whole chickens!) from National Geographic. Their backs are an olive green with black markings; the coloring fades around through orange and yellow-green onto their bone-white bellies. There are lots of colors splashed around on individual scales; I mostly represented them with dots of a couple different dark colors.
I dunno how long it took me to do them; I spend a lot of time figuring out how to do the first one and then paint the rest relatively quickly.