You would have to have Partridge hiding under your boy too - its recessive and will only show up with two copies - one from each parent. Lots of Blacks are hiding Partridge, and some will even LOOK partridge-ish when born - and then turn solid black when full grown. Those birds have Partridge genetics but enough extra melenizers to completely cover it... Your baby may be Black when grown up.
On the Self-Blue (Lavender) thread there were faintly Partridge marked chicks that grew up to be solid Lavender. Those I would guess are based on the Partridge base, but the adult feathers show no signs of it. Just another example of the amazing genetics pool hiding inside our "Black" birds. My Lavender Ameraucanas did not look Partridge at all - they are based on E (Extended Black) and not eb (Asiatic Partridge).
Two copies of Dominant White will not always give a completely White bird - because there are still leakage possibilities (even White Leghorns will have a black feather every once in a while). However, two copies (homozygous) being bred over and over again will eventually wipe out most of the black spots - which is why you need to keep going back to Black to keep Paint. Also, if you have a bird that only has one copy of Dominant White you will get some Black birds from that pairing (50% chance). Since our Black is not based on Extended Black you can have all sorts of oddball colors showing up in Paint Breedings. When breeders get a solid Dominant White based on pure Black and get a pure White homozygous bird - then you might get solid White birds all the time from homozygous breedings. Not from the stewpot of genetics we use for Black Silkies though... probably why it is still a "work in progress"
