Are a cat's anal glands supposed to look like they have dark stuff inside?

[Shaunte]

My cat's anal glands almost always looked like they are plugged up with dark stuff (compared to most of the rest of her skin and orifices in that area which is very light pink or white). I recently had her groomed and part of the grooming was anal gland expression but her anal glands still look plugged up with dark stuff. The area doesn't appear swollen and my cat isn't scooting or licking her butt anymore than I've seen other cats doing. Did the groomer really express the anal glands? Wouldn't that have caused the dark stuff to come out? Or is it normal that the anal glands are filled with dark stuff?