|Dark Traditional Siamese Cat photo by iamcootis on Flickr.|
I am guessing that this nice looking traditional seal point Siamese cat is old. I make this assessment on the basis that he is fat - no..only kidding. It is because he is very dark on the torso. Although older cats have a tendency toward obesity until they are very old when they lose weight.
His torso is almost as dark as the points (the extremities).
This darkness of the color of the hair where it should be creamy white is due to the skin being colder in that area than it would be in a young cat.
When the skin is cool at the extremities the pigmentation - melanin - is created in the skin. Where the skin is warmer in the center of the body it is not created - usually - unless the blood circulation is poor due to old age when the skin is cooler in the center of the body as well.
Interesting point: very old cats are less likely to get fleas because there is less blood under the skin due to poor circulation.