In the 1980’s the Blue colour in the staffordshire bull terrier was a fault, as was the black and tan coloration. I personally think colour is irrelevant as there are far more important factors to consider when looking at the quality of a dog than colour.
However the Blue staffy is produced from recessive genes and as such they were rarely seen. The legend was the Blue was a throwback to when the Blue Paul was bred with Staffies in centuries gone by.
However from being a rarity in the 80s , now more than 75% of the Staffies bred in the UK are blue. To get this you need a minimum of both parents being recessive Carriers of the gene, but as such a significant percentage of pups are blue the likelihood is the majority of them are Blue to Blue breedings.
There are problems that arise from this. Breeders are narrowing the gene pool artificially within the breed. Focusing on colour first ( and they have to be to get so many Blue dogs ) you are ruling out more important traits in good dogs simply because they are not blue.
The Blue dogs being bred to such an extent will lead to less and less of the other colours. Blue to Blue only produces Blue. Breeding for colour doesn’t improve dogs and they are just another way of producing designer dogs.