Male rat as discolor fur?

is it a bit orangey?

if so, it's buck grease. male rats have oilier coats, and sometimes on light coloured animals this can cause staining.

If your rat has recently had diarrhea, it could stain his fur, but I doubt it would be there for two months. Rats also secret a substance called porphyrin that is an orangish red color. This is easily seen on white rats near the eyes and nose.

Also, if you got your rat as a baby, their coloration changes when they get older. If your rat comes from parents that carry a 'point' gene (a gene that causes colored spots or smudges to appear on the nose, base of the tail, ears, feet, and sometimes eyebrows) he could wind up with some pale markings in addition to his spots that look like those of a Siamese cat.

http://www.afrma.org/rataocp.htm these markings can be seen here on the first and third rat from the top.

You should monitor your rat, and if he is passing solid stools (no diarrhea) it is probably just his fur darkening as he grows from a boy into a man. xD

I agree with Sheena. Sounds like buck grease. If its really bad, give him a bath with baby shampoo, or shampoo for rats. Be careful not to get his face and ears wet! Its normal, and nothing to worry about. All males have it, and its especially visible on white rats. :)