In haircoloring, 'tone' refers to:

Tone refers to the warmth or coolness of a hair color — for example, golden, copper, and red are warm tones, while ash and blue-based shades are cool tones. Tone is distinct from level, which describes lightness or darkness. Both level and tone are needed to describe a color accurately and to formulate results. Understanding tone (and how complementary tones can neutralize unwanted ones) is part of color theory tested on the exam, though detailed formulation is learned through training and practice.