Hue, that is whether something is red or green etc is easy, most people can see that, but tone and chroma take considerable training before they become ‘natural’ for the eye. Tone is simply how light or dark a hue is, sort of like converting a picture to black and white. While difficult to ‘see’ tones, tone is the single most important aspect of colour, and mastery of tone allows the illusion of light. Chroma is how ‘neutral’ a colour is and is usually achieved by the addition of varying amounts of the complementary of a hue. Thus a natural green for foliage is often arrived at after a small dash of red to a green.