Andalusian blue has a darker head, hackle & (for males) saddle. Self-blue and lavender are the same--at least in the US. The name of the gene is lavender, designated lav. It is a recessive gene, meaning that each parent must contribute a copy for the offspring to display the characteristics. Yes, it is a solid, light blue colour. If both parents are lavender, then all offspring will be lavender.
However, from your clarification of what you get (blacks and white with black specks as well as the blues), you have andalusian blue, not lavender. The blacks are black, the greys are blue and the whites with black specks are splash.
However, from your clarification of what you get (blacks and white with black specks as well as the blues), you have andalusian blue, not lavender. The blacks are black, the greys are blue and the whites with black specks are splash.