The recessive blue is black based with the recessive slate factor slsl. Genotype BB slsl.
A true breeding variety.
These are nearly identical in phenotype to the dominant slate version called lavender (aka self blue) with a genotype of BB DD, but the recessive blue carries an entirely different slate factor which is recessive.
One big difference in breeding these to non-slate birds, unlike the self blue, is that the recessive slate color will not express in heterozygous form as dominant slate does. For example, breeding a recessive blue to a black would result in 100% black offspring, but all would be carriers of sl.
On the other hand, if you bred a lavender (aka self blue BB DD) to a black, you would get what is known as slate (aka blue slate, BB Dd), which have random black splashes. This is the heterozygous form of dominant slate on a black base.
Newly hatched recessive blue poult