Not exactly sure on blue, but you may well be right. I know chocolate and seal are like that.

What I do know is, because black is dominant, if it is present in the dog then it is physically expressed, meaning the animal is black (even seal and chocolate are forms of expression, albeit diluted).

If the color black is not expressed, then it has been lost. This can happen if a black dog with a recessive gene mates with a red/buckskin dog with a recessive gene, and the recessive genes are what pass on to the pups. In this case, the black is lost and only then can the recessive color traits be expressed.

Jack