I believe that silver and Italian are different, so it should be okay to breed silver to Italian. I'm not an expert in the genetics, though, so I could be wrong.
Southwest Gamebirds has a whole study available on the genetics of the fee. I have not really studied it, but I know that one copy of the gene will wash out the colour, while two copies will remove the colour, and you end up with black and white birds.
As for lethal genes, the ones I know of...