Monochromatic

[Sarah]

Consisting of one color, or presenting rays of light of onecolor only. Monochromatic lamp (Opt.),a lamp whose flame yields raysof some one homogenous light. It is of great importance in opticalexperiments.

[Sarah]

A personality type which is incapable of processing a broad spectrum of thought and only perceives issues in an all-or-nothing black or white context. Closed-minded. Obtuse.

[Jason Yan]

using only black, white, and grey, or using only one colour:

[Little_Girl]

Containing or using only one color.