YYMM, Cadmium Red Light, Opaque.
|I use cadmium Red Light as opposed to Red Medium because Red Light happens more often in nature. It's easy to make a Red Medium hue by adding a little Magenta to it, but it's impossible to make a Red Light by adding Cadmium Yellow, because it becomes pasty looking.
A bright, permanent, opaque, non-poisonous red paint more saturated than Cadmium Red is called DDP Ferrari Red, PR:254. Pyrrole Red PR:254 (opaque or transparent) may be the same color.
Being a secondary color opposite Thalo Blue it is useful in making a very dark cool neutral often happening in the evening. It is very dense, permanent and opaque. I haven't tried the transparent mixture yet.