Finally figured out what this pattern is. The AFRMA calls it "Splashed". A very cool pattern, indeed. This, apparently is the classic version, although it comes in a light phase. I have a female now that is a Dove Gray Splashed...I'll have to get a photo of her. The guy in the picture is all grown up now and soon to be siring little mouselets of his own.
In my colony it seems to be a simple recessive single gene. Anyone knowledgeable in mouse genetics know for certain?