Stress Marks?

[SierraandRhonda]

My Sierra has had a black thick line across its beard for over two weeks now. I am unsure if I have a male or female....there is dark almost circle markings all over its tummy. Is this stress marks or more colour coming out (lately Sierra went from dark to bright yellows and kinda oranges) any opinions welcome

 

[Bellalee]

I think they are stress marks.

 

[SierraandRhonda]

Is there an easy way to tell what is stressing him out or is it leave him alone for awhile and see what happens?