Thalo Green, the color between Cyan and Yellow is a transparent color,
it's opposite color Magenta is transparent also.

It takes two transparent oppositions to mix neutral,
or
one transparent and one translucent color,
or
two translucent colors,
or
one transparent and one opaque.
Two opaque colors just won't do it.

Top-tone is adding White to the color.
Under-tone is adding clear.
Mass-tone is thick out of the tube.
Transparent is clear, like colored glass crystal or Easter egg food coloring.
Translucent is floating colloidal compounds of colored elements.
Milk is translucent.
Opaque is dense and light blocking, like a rock.
YYYY = As Yellow as you can get,
YYMM = Yellow and Magenta, as Red as you can get.
MMMM = pure Magenta
CCCC = Cyan
This is the normal afternoon darkest shadow color combination of colors.
Mornings would use a Brown and Ultramarine opposition.
Thalo Blue and Cadmium Red opposition happens in the evening.