Sanna, that is a loaded question about what goes into a paint breeding. I know that the white they are using is a dominant white-- which pretty much the white silkies everyone has is not. The paint (black spots) are supposedly caused by holes in the pigment... but I know that theory is still trying to be tested and figured out. I haven't done much reading on it, but it doesn't sound easy at all. And no, they don't breed true. And apparently you aren't supposed to breed paint X paint --- but have a black (a REAL solid black) over paint. Finding a good black isn't easy. How many pictures do people post here of their "black" birds that are really blue? All the time. Are you sure the P wasn't for Partridge? Especially if you got a partridge out of it?
I got shipped eggs not to long ago and one was labeled BS (blue/or splash) and I hatched out a partridge. Mistakes happen...
Anyway, read this thread:
https://www.backyardchickens.com/t/429754/the-american-paint-silkie It is the paint thread set up for silkies. Reading the background and seeing how they are working toward paints is very interesting, but it also sounds like you need a PhD in genetics! LOL Sonoran is breeding paints, too. She has a really amazing paint in her avatar.