Revlon Professional Revlonissimo Colorsmetique Permanent Hair Dye 10.21 Lightest Iridescent Ash Blonde 60ml (2.03floz) UK Delivery

The numbers on a hair dye identify its shade. The first number is the level, which shows how light or dark the color is, on a scale from 1 (black) to 10 (lightest blonde), with some brands going up to 11 or 12 for very light blondes. The number after the dot, comma, or slash is the tone, or reflect: most brands use 1 for ash, 2 for iridescent or violet, 3 for gold, 4 for copper, 5 for mahogany, and 6 for red, while 0 means a natural tone. So a 6.3, for example, can correspond to a level 6 (dark blonde) with tone 3 (gold), making it a dark golden blonde. A second tone number, like in 6.34, adds a subtler secondary tone, and a 0, like in 6.60, makes it more intense.

Not every brand uses the same system: the same number can stand for a different tone from one brand to another, and some brands use letters instead. The shade information each brand gives for its own hair dye is always the most reliable guide.