"Monochrome" is an ambiguous title.
As you can see, more than one color and shade are represented here. Some photos warrant a sepia tone, some a basic 256-shade of grey palette and others selective muted colors.
But in each case, the colors and shades of the photo are captured and adjusted in order to suggest to the viewer that the main theme of the photo is the subject itself and that color only distracts from that theme.
Sabi can be well-illustrated in monochrome captures.
Wabi and Sabi
