Unusual cat breeds/colors

[freckledimple]

This is more of a breeding question than a breed question. We have a new kitten, and the vet said he had never seen the color before Runt is black pointed with a dark silver-tipped coat(so far); he's only six weeks old I was wondering what genetic combination had to occur for this to happen. Of course, he may be a mutant

Here's some pics: