I just read about the siamese gene c(h) in rats, and it was just interesting, I wanted to let ya know why they dont produce that seal color all over.

The science stuff:
The tyrosinase enzyme converts tyrosine (colorless) into dopaquinone (colorless). Phaeomelanins (red to yellow pigment) are made out of dopaquinone.

A mutation of the tyrosinase enzyme caused by the chinchilla gene creates the albino (CC) and the siamese (c(h)) by making it semi-functional.

The semi-functional tyrosinase is very fragile and temperature dependent. When it is too warm, the tyrosinase breaks, and it will no longer convert tyrosine into dopaquinone, which means no more phaoemelanin (red yellow) pigments. That is why the pigment is only created in cooler extremities of the body. (so why isn't the body black? Because dopaquinone creates the dopachrome to create emelanin (black brown) and the tyrosinane can't be converted to create it by the chinchilla gene)

When you mix the dilute gene into the siamese you get blue point siamese.

(The dilute gene is a mutation that literally stops the pigment from reaching the cell edge, creating the "steel blue" color.)

I don't know if there is any way to really stop the eumelanin from being created in the extremeties. Because a fawn or yellow point rat would be totally cool.

Hope it wasnt to muddled to read!