Why Is One Of My Bristlenoses Darker Than The Other?

[orange shark]

Hey,

I have just realised recently that one of my bristlenoses is a much darker brown than the other one. Does this mean they are different sex? I have my suspicions that they are not ancistrus sp. 3 which I first thought and I am thinking they are now Ancistrus tamboensis. Im putting on a picture if it works and if the pictures any good could some pleco expect confirm which type of bristlenose it is

Here I go...

http/i197.photobucket.com/albums/aa216/o...e_shark/008.jpg

 

[smithrc]

slight shade variations are normal... I'd be willing to put money on the fact they are sp3... there can be a lot of variation from one fish to the other.