Dark pigments not work with Elemental Genesis or tips wrong?

[LYNX]

In-game description: “If you stack all 4 dark pigments, ANY spell can consume them for +300% damage”

I stacked all 4 pigments but the Elemental Genesis remains grayed out. Because -

Game Description: “Genesis of Elements can only be cast with all 4 different elemental pigments.”

But at the same time it can be cast if you have ANY light pigments, even if ALL 4 are light.

Why light works, but not dark?

[Rai]

Not really
Light stains are used as a substitute for any stain requirements hence you can cast genesis with 4 light stains.
Dark stains aren't used as substitutes, they don't trigger the stain consumed effects. The effect to consume 4 dark stains to increase the damage is purely the weapons effect but you don't get any stain consumption benefits like typhoon lasting an extra 2 turns it just boosts the damage.
Genesis is different than every other spell because its the only spell that requires you to have those specific stains or otherwise light stain to even be useable.