Ghost shrimp can't contract ich. They can be carriers--the spores can get caught in their shell, but the shrimp is not actually infected. Some variation in the coloration of their shell is normal.
If it's a big concern, quarantine the shrimp without any fish for 4 weeks. Ich can't survive without a fish host and will die off without producing a cyst (sorry--correction--they aren't really spores).
