Ohh interesting question! I think I would assign ultramarine to my art. I know if I tried to put all the works I ever made into a blender, I guess a grey blob would come out, but many of my favourite paintings of mine had ultramarine somewhere in them. It reminds me of highschool days walking alone to the bus station during after school under a clear blue june sky. It imitates darkness, it's a saturated dark, and a warm-cool color. It makes things pop out, it makes for an excellent reflection, it burns itself into your eye. I have no idea how to classify it properly and it confuses me but it works, I guess just like my art sometimes :)