I assume the bright stuff can't be blown off with a pipette and we are looking at bleached coral tissue or even skeleton shining through?
In that case the coral might be doomed. It has too much/little flow/light, isn't happy with the water parameters, or has some infection that would require appropriate treatment, I suppose
If however it's just some mucus it uses to keep food in place, its fine. Under blue light it becomes even more difficult to differentiate.