Reasons for black beard?

[Monkey]

Herculette rarely black beards, if she does she's usually angry about something.
Now Monty is black bearding, he's looking at me and being black bearded...

No stressmarks, other than that hes his regular color. He has eaten, had his bath, he's now in the cool end of the tank.
He seems content so why the black beard? Hes not bopping or anything..
What is the different reasons for black beards? show off? attention? anger? random? all of the above?

 

[Claudiusx]

Territorial, breeding, angry, threatened, to look intimidating, and probably some more I can't think of.

-Brandon