what is diference between neutral darks and shadow?

Answer 1

Real Opposition Pigments Make Neutral Darks

These six opposition colors are the basis of all dark shadow colors when you don't use black pigment.

Cadmium Yellow Light and Cadmium Yellow Medium are opposite Ultramarine Blue.
Cadmium Orange opposite Cobalt Blue .
Burnt Sienna opposite Cobalt Blue.
Opaque Cadmium Red Light or Dark are opposite Cyan which is called Thalo Blue.
Quinacridone Magenta Transparent, PR122 only, is opposite Thalo Green.
Purple and Yellow Green are opposite colors. Green Oxide Opaque is dark yellow-green to use as the opposition color.