Black nickel plating is rainbow color in high current area

I request please give me answer to some problems
black nickel plating problem is high current density rainbow shades
pls give me answer

Black nickel is a regular nickel solution that is poisoned by another material to get the black. Many alloys plate in different ratios at different CD's. Black nickel is well known to be fussy about the temperature and the CD that it is plated at to get a nice matte black.

Consider plating the part at a lower amperage or use robbers in the area of high CD's.

Do these rainbow shades appear after your rinsed them or after you dried them? As it can happen if you dry them to warm, or your rinsing fluid is not clean enough, or another thing is you did not etch the surface well enough, perhaps too long ?