A quiet conversation in the darks, is the dark marks or shapes that are within the larger dark areas of your art. For example, if you’re painting a white bird with a dark green jungle background, then the dark tree branches and dark leaves, would be the quiet conversation in the darks. Those leaves and the tree branches are very subtle, as they are all dark values within a jungle background that is also dark in value.
On the right side of the diagram above, the smaller triangle, star and circle are the quiet conversation, because they are close in value to the black shapes they appear upon. The close value relationships of the quiet conversation can provide subtlety and sophistication to your art.