I've never kept crayfish, but you could try switching out your light bulbs to ones with a higher color temperature. I have an 18000 K bulb that makes everything looks ridiculously colorful (but it also grows algae far better than plants).

 

In SE Asia they are farmed in ditches full of hog effluent so maybe really poor water quality is the key to keeping them blue.

 

If they were Procambarus Allenii the red brown sounds like a wild type coloration. When I had Allenii they stayed bright blue no matter what I feed them, or the substrate or the lighting.

 

I thought blue coloring was a genetic thing. they molted several times before changing colors.

 

My understanding is that most freshwater crays prefer to live in really murky water and this will affect their colouring. When i was a kid i used to catch yabbies (cherax destructor) in the creek near home and i had 2 good spots one was crystal clear water and the other you couldnt see your hand 6" under water in the clear water they were jet black and in the murky they were blue, brown and olive green, both of these spots were on the same river system just a couple of kilometers apart.

try adding some driftwood and letting the tannins leach into the water and see if that changes anything?

good luck
Jack

 

I never have this problem before though.
Kind of weired to hear that it changed color.

I had one before and it molted many times without changing blue till one of my staff accidentally stabbed it to death with the pole it was hidding in.

I saw bright orange and bright red version before.
They are very nice if the gravel and background is black.

 

I read around more.

the problem is LFS and their suppliers selling false blue crayfish. they knowingly will change color later.

a true blue has genetic issues that force it to be blue due to enzymes or something (can't remember exact reason) and due to that they will actually get more blue the older they get.

anyone reads this and wants one do some shopping and find a private seller who breeds true blue crayfish or a LFS that will take it back if it changes color.