Old Holland Yellow-Green Organic Opaque.
This is a color that is easy to make but easier to buy.
A color that I use in every landscape painting either pure or in mixes. It is very dense, permenant and opaque. It's the same color as Brilliant Yellow-green in acrylics but made with organic pigments.
A split-complement could be made with, yellow-green, cobalt blue and cobalt violet, they just happen to be three opaque colors, the complement color is ultramarine violet.
Either of those sets of colors will combine to a neutral dark or look good together.
That's for the interior decorators out there or those that mix and match colors well.