Jackie Simmonds always said "If white is not light enough, you need more darks."
It was one of her best pieces of advice.
I prefer using other darks to create a complex dark passage. I am currently working with very dark: olive-y green, purple-blue and wine red; these create a dark that really works- and also allows me to echo those same hues in lighter passages for a cohesive colour scheme.
But I work in layers and layers of colour in soft pastels, not in a one-layer, direct application of oil paint, so mileage *must* vary.
(I cannot imagine not having the Get Out of a Mistake Card by only using direct application- I'd have to switch to, like, charcoal; it's something I admire in those who use that process- so well done you, Wayne! To me, getting what I want is like cooking: You keep adding and balancing and heating until you have the flavor you want. At first, lots of mistakes, but as you learn how colour works in soft pastel [which are pure pigment made into a paste (pastel) and rolled or pressed into stick form] it becomes far easier to get what you want, hue and value-wise).