If you've got more yellow than blue, you get a yellow-green. And, conversely, if you've more blue than green, you get a blue-green. Another fundamental concept, of that of complementary colours. On the colour triangle, the complementary colour of each primary colour is the secondary colour opposite it. So the complementary colour of red is green, of blue is orange, and of yellow is purple.
Complementary colours are just that, they complement or harmonise with each other.
So by adding a green near a red, it makes the red seem more intense, while at the same time toning into the green, creating that feeling of colours that work together. Colour theory also talks about warm and cold colours, which are meant to advance and recede as you look at them. It will still look like a shadow, but instead of being a flat black, the complementary adds depth in the shadow and lifts the primary colour. The same for white, teach your brain to think of a very light complementary instead of grabbing for a sanitized white. Another possibility to consider instead of simple black and white is using a textured black or white fabric as the light falling on this will create additional shadows, adding to the feeling of depth and life.