Cleaner Shrimp's Black Belly

[Mikey B]

Hi Everyone. Need your opinions.....
I have two cleaner shrimp in my tank.
Up until a few days ago, they both had a "transparent" lower belly/tail.
Recently, one has developed something very dark in its lower abdoman.
I thought it could be eggs, but I'm too new at this to really know.

Any ideas what the dark stuff is?

Thank you.

Mike