I would remove the black shrimp, maybe set up its own tank so that if any more appear you can try to breed them to throw true black, true in that all their offspring are black and not a rainbow of mixed colours.
If you leave the black cherry shrimp in with your reds unfortunately the colour will muddy the future offspring and what can happen eventually is the shrimp will start throwing near wild type cherry shrimp.
Sadly all cherry shrimp colour morphs will and can cross breed because they are in reality all the same shrimp just different colours.
I have heard of people keepking a tank of mixed colour cherry shrimp and not being concerned about the resulting hodge podge of offspring, but I think eventually the novelty wears off, especially when your trying to remove the wild colour and trying to maintain the reds, yelllows, oranges, blacks, greens, blues and rili's in the mixed collection.