Well if you breed your leatherback you will "in theory" get 50% leathers and 50% normal's. The color of them is not genetic and the babies will look like a mixture of their parents colors. If you get a silkback and breed it to a normal you should "in theory" get all leathers but i guess breeders are saying you get some normal's but mostly leathers.
If you breed a male leather to a female leather you will "in theory" get 25% silks, 50% leathers and 25% normals. If you breed a male silkback to a female leather "in theory" it will be 50% silks and 50% leathers.