DIRTY COLOUR
From Colour: A Manual of its Theory and Practice

(reconfigured)

Dirt has been well defined as “matter out of place” and this is singularly true in the case of colour. The sense of dirtiness is generally due to a failure to observe the passage of grey. In considering so difficult and delicate an issue as this, one must take the trouble carefully practice fine and slow gradations. One can obtain thereby quite rich an effect with a much more powerful and dignified handling. The nearer we are brought to neutral grey the more nearly do we become harmonious, but take warning that it is fatally easy to look dirty. Grey which touches of another colour have been allowed to appear will surely look dirty and what ought to be quite silvery only succeed in looking cold and dowdy.