They were in a litter of 4 - the black one has a little white bib / vicar's collar, and the other brother (who now lives down the road with a friend) was pure black. We were pretty surprised by the variation in colours, from the mother, a pure black street cat who decided to move into our house when she got pregnant.
Haha, thanks. Shame it's a fairly low quality phone picture, but I could still print a smaller version :) There's a reasonable chance they'll do similar again, and i can maybe get a photo with my good camera - one or two stretching out on the steps like that is fairly common, so maybe it's just a case of bribing the other one with treats.