Be wary the dreaded BLACK
Watch the above video first
Yes, keep that fiendish colour well away from your palette lest your mind take a Lovecraftian trip into insanity.
Seriously though it is far better to mix those darks yourself using a primary colour with it's secondary colour:
Red + green // blue + orange // yellow + purple.
Using a limited palette and mixing colours makes for a far more harmonious painting too.
You don't want to end up a fly trapped in a bottle of shadows!