A colour has three essential properties; hue, intensity and tone.

Hue: The precise definition of a colour is only possible by quoting its mathematical frequency of vibration. For instance Red is a vague term, for it may lean towards either scarlet or crimson. Fortunately artists do not need to describe their colours in words and, in industry, colour charts are used. The important thing for us is to be able to feel the subtle changes of hue that occur within a broad definition.

Intensity: The purity, brilliance or saturation of a colour, e.g. cadmium yellow-mid is a much more intense pigment than yellow ochre. For any given hue an infinite variation in intensity or purity is available and this property should not be confused with tone

Tone: The position of a hue on a scale between white and black.

It is important that we are able to differentiate between these three properties. Inability to do so is the prime reason why so many student works have flat, lifeless light passages and chalky, dead darks. One school of painting dodges the problem by advising that we always work in the middle tones, but when you compare the short tonal range between pigmentary white and black with the light of the sun and our darkest night, obviously we need to be able to use our pigments to maximum effect.

In fact these three properties are interdependent. Yellow is at maximum intensity in a high tone while violet is at saturation in a low tone. Colours at maximum intensity conform to a tonal scale as follows; White, Yellow, Orange, Green, Red, Blue, Violet and Black.

A few experiments with your most vivid pigments that conform to this tonal scale will show interesting results. At maximum brilliance and in correct tonal order any two can be used in vibrant harmony.