Lemon Yellow Lead Chromate, opaque, is a highly calcimined lead pigment. It is the very coolest Yellow and is opaque. It's modern dry chip color replacement is the translucent Hansa Arylide Yellow.
We as artists should like the return of Lead Yellow as there is no color like it.

To make the darkest neutral dark color mixtures, at least one of the two colors must be transparent.  As in the Cadmium Red and Thalo Cyan Blue opposition. Two opaque colors won't mix as dark, as with Cadmium Orange and Cobalt Blue.

To mix a neutral dark with yellow opaque is impossible.
You must use the dark hue of this yellow color, Burnt Umber. Burnt Umber and Ultramarine Blue mix to a neutral dark. tint any neutral dark color for a full range of neutral grays.