I'd please

[snake65]

I have a few of these pop up, some have orange and some have green around them. They are flat very dark maroon colour and don't move.
Tia

 

[reef lover]

#reefsquad

 

[Ron Reefman]

From that photo and lack of other info; I'd say it's almost impossible to say.

How long has the tank been set up and running?

Is this live rock from the ocean that was new?

 

[Eagle_Steve]

I have a few of these pop up, some have orange and some have green around them. They are flat very dark maroon colour and don't move.
Tia

Can you get us a pic of it with less blue light and more white light?

 

[KJ]

Look like some kind coralline algae.