Peppermint Shrimp turning dark/black

[legaultrm]

Two of my peppermint shrimp have started turning dark/black at the tail. The body gradually turns darker towards the tail, and the tail is almost black. I have checked my water parameters, and all are near or at 0. One has since died, but I noticed the second one today. Any ideas as what could be happening? Unfortunately I don't have a camera handy to take a picture of this.

Thanks,
Raimie

 

[Tennyson]

I'm pretty sure this is normal. It's all part of the shrimp getting older.

As it matures, it becomes darker, red lines become more defined, and it's tail turns into a dark brown/black. Atleast, thats what happened with my pair.
Are there any signs of illness in the shrimp?