Dilute tortoiseshell is a coat pattern, not a breed. Where a standard tortie mixes black and orange, a dilute shows blue-gray and cream in patches or a fine marbled blend. The pastel shades come from a recessive dilution gene a cat must inherit from both parents, and the patchwork depends on two X chromosomes, so nearly all dilute torties are female.
Most are domestic shorthairs or longhairs, though the coloring also appears in Persians, British Shorthairs and Maine Coons. Coat color says little about personality, despite the tortitude folklore. Dilute torties can be shy, outgoing, cuddly or independent, so spending time with the cat tells you far more than the color. In Philly, where many cats live in rowhouses and apartments, that fit matters more than the pattern.