To the best of my knowledge there are two acknowledged types of blue.
Self blue, a recessive trait.
And the more common andalusian blue, with it's blue/black/splash possible variables. I suspect there are multiple modifiers that can affect the hue and clarity of the blue, or splash.
Correct. And both of those genes are really more modifying genes rather than color genes. Both types of blue genes dilute black feathering, changing it from black to shades of grey. These 'blue' dilute genes can be applied to just about any 'pattern', from barring, to solid black, or even to partridge-type patterns.
Self Blue/Lavender will dilute red/gold color, too, turning it to pale yellow.