The colours are chosen according to mass tone (colour from tube) undertone (bias of colour when in a thin film) colour strength relative opacity and the character of the pigment in water colour ie. granulating staining or even wash. The resultant colour spectrum ensures the largest number of colours can be mixed from the range. The optimum brilliance of every colour in the Artists' Water Colour range is unparalleled by any other water colour. Remarkably this brilliance is combined with high permanence.