Poor nutrition usually is the cause of OEBT discoloration, (Assuming it was deep blue as an adult)
I believe it is one of the trace minerals that they add to the food that account for the blue coloration, but I forget what.
Other causes could be pH is too low, OEBT like a slightly higher pH than other Card. shrimp.
Might also be stress from ammonia or temperature.
I assume you mean Caridina and nor Cardinal. Anyways, OEBT like neutral water while Bees like slight acidic (6-6.8?) water.