This article describes the term colourfulness and its relation to chroma and saturation, and gives evidence that subjects can scale this attribute more easily than the other two. This ability is used to generate grids in Ç92 Ç93 color space based on hue and colorfulness by subjects who are adapted to either Illuminant D₆₅, D₅₀ or S_a. These illuminants represent two typical versions of daylight and an incandescent source. The grids can be used to predict changes in the appearance of colors when the subject is adapted to these different sources. -- AATA