Hello. When I post pictures of my common BN's I get posts saying that they look 'stressed' due to light brown patches on the fish. They've been like that as long as I've had them, so could someone please tell me why they are stressed, or what the causes are?

ummm, stress

high temp, low temp, high nitrate ammonia or nitrite, too high pH, too low pH, other incorrest water parameters, too much light, too many other fish, too much movement around the tank, being pricked on by other fish, being handled too much, poor food, illness, not enough hiding places, wounded or maybe its just a nervous fish

or it could just b that its a light coloured fish. there are some for some reason that are just lighter than others. I have some that are almost black while others are so light they look yellow. just they way they go.

I agree with the guys, they can change their colour depending on mood, If you have all their needs covered &
If it has been this colour for months n months, I'd hazard a guess that is their actual colouration , A clear photo would help us...