Well to answer questions...he is taking scented mice. I bought a bunch of catfish to feed him but found out that they too contain thiaminase...which sucks...because I could have gotten perch or bass instead and those would have been fine. He did eat a few fish and I didn't notice a real problem as far as stinky poops or anything, but he readily takes fish scented mice and I imagine after a while, he'll take unscented....might throw him a fish now and then to get rid of them just for fun.
As far as dying him green and putting him in a maxwell cage, I've got a room full of green snakes in maxwell cages...don't need another

Just for the record...watersnakes are NOT cottonmouths...watersnakes are non venomous snakes and cottonmouths of course are venomous. Switching their cages though has made a difference. My cottonmouth was not eating in the other cage and he took a meal this evening in his new, smaller cage. Once he's out of quarantine, he'll be in one of my smaller custom cages and I think that will suit him beautifully. He is otherwise and easy snake. Works well on the hook and takes a lot to get him striking at something.
My watersnake has not tried to bite and is actually pretty good when handling him. He's a bit squirmy to be sure, but no musking and no biting. I found one in my backyard a few months ago and it tried to bite me once when I first caught it, but after that it just hung out. I find they do calm down with gentle handling and mine is starting to figure out that nothing happens to him when I open cages and often there is food...he's an eating machine!
When I first got him I fed him a live goldfish to see if he'd eat at all and then try to tempt him to take a mouse (didn't work by the way) but it was fun to watch him hunt the fish and change his hunting technique to suit the water bowl size. They are pretty smart!
Now that I've figured out how to scent his food (just put the thawed rat in the bag with a catfish) he's chomping down like a champ. Today was the first time he took it by the head...they tend to grab mid body first and they are super fast eaters. Good fun! I like em!