Hello, a black moor should have hints of bronzes in coloring.
When upgrading 29-55gal 2×fantails,1×moor, 2×dojo loach I suffered a mini cycle. I only realized this when moor started turing bluish grey.
Good bet its water quality. I would test then do 50%water change at first then 25%every 2 days. See if color changes back. Water should test 0 ammonia,0 nitrites & below 40nitrate.
A moor min tank sz is 20gal for 1 & 10gal each additional. Its temp should be 62-72°. It would be good idea to feed peas, cucumber or anacharis plant(some type ruffage in diet) to elevate swimming issues that might occur. (Gobble in 1.5gal qt)Hope this helps you.