Step 1: Understanding the Concept
The question asks for the definition of "Monochrome". The word comes from Greek: *mono* means "one" and *chrome* means "colour".
Step 2: Detailed Explanation
A monochromatic colour scheme consists of variations of a single base hue. These variations are created by changing its saturation and brightness. This means using one colour along with its tints (adding white), shades (adding black), and tones (adding grey).
(A) Mixture of colours refers to a polychromatic scheme.
(B) Thickness of colours refers to texture, not a colour scheme.
(C) Different tones of the colours (plural) implies using multiple hues.
(D) Different tones of the same colour accurately describes a monochromatic palette.
Step 3: Final Answer
Monochrome means using different tones, tints, and shades of a single colour. Option (D) is the best description.