With the 21w10a release, a new variation has been added to the silverfish block. Silverfishs can now also spawn inside deesplate blocks.
The textures of the silverfish are gray as they emerge from the stones. This is because they are camouflaged to keep up with the environment. The newly arrived deepslate stones are disrupting this situation. Don't you think a gray insect emerging from a black rock is ridiculous?
This is some kind of visual bug. The solution would probably be to add a new variation for deepslate silverfish.