My roommate is at her wit’s end trying to tell apart her two albino white mice. I tried cherry juice last night, but the mouse licked herself clean after an hour or so. Are there any mouse-friendly stains or dyes that might last a bit longer?
(This isn’t the strangest thread on the Dope this week, is it? This is the Dope. There is always something stranger).
Standard food colorings? Those seem to stain human skin pretty well in my experience, and should be nontoxic in the amounts you’d need.
I am sure your local pharmacy has a beauty supply section that can help.
I’ve used a Sharpie on a chinchilla before.
Shave the hair a little on one of them?
Need answer fast?
Sharpie dot on the head. If they are housed together, keep them apart until the smell is gone, (overnightish) or mouse #2 may try to chew the offensive stuff off.
Not safely. Hair dyes have all sorts of powerful chemical crap that would probably peel the wee mousie’s skin right off.
Do NOT use chemical hair dyes on pets.
You could try a spot of turmeric dissolved in water to make a paste and use that. Turmeric stains are a bugger to get rid of and is a mild spice used in Indian cooking. I use it in almost every other dish - so it probably is quite safe.
I was also going to suggest beetroot juice.
Kool-aid minus the sugar. Works on cats.
And humans. 
I would suggest either full-strength beet juice or pomegranate juice - I’ve had both stain my skin for significant periods of time if not promptly cleaned off, and they’re both food items so non-toxic.
Or soak the outer skins of yellow onions to get a yellow dye, or a green dye from spinach or similar green veggies. Concord grapes will give you a nice purple color, or cherries, blueberries, or blackberries will produce good dye.
I agree with Broomstick that it’s safest for the mice to stay with dyes like this, based on food products. The only problem might be that the other mouse will try to lick it off, if you don’t wait long enough for it to dry. But that just means reapplying it more often.
Why does she need to tell them apart? The closer one is “this mouse” and the other one is “the other mouse”. It’s not like she’s going to train them to answer to their names or anything.
Yeah, I came in to say just this. Is she performing some kind of behavioral experiment with them? What’s the point, isn’t that why you bought two identical albino mice anyway, so you can have a backup?
Why not just tie a bow or get a tiny collar/belt to fit around one of them? Some thing that they can’t chew off. (See the scientist in me just says tag one of their feet with a metal band, but I don’t know how pet owners would feel about that).
Safe and no need to continually re-stain the mice with.
Though why you need to tell apart the two mice, I’m not really sure, then again I think I kinda get it. We’re all wierdos like that says the man who named each of his mp3 players.
Cut off their tails with a carving knife (but to different lengths)
Well, actually, we’re trying to figure out their personalities. Is Sophie the brave one and Alba the shy one, or are we looking at different ones each time?
Also, quoth the roommate, “They’re different people with different names.”
But first you have to get a third mouse, then blind them.
I’m gonna guess that whichever one keeps getting grabbed and smeared with beet juice ends up being the shy one. Classic observer’s dilemma: you can’t do the observation without affecting the result.