Depth is given a whole number from 1 to 10, where 1 is the darkest hair colour (black) and 10 is the lightest (lightest blonde). Some manufacturer’s also use 11 and 12 on their colouring products to account for the blondest of the blonde.
These 'Base' colours are used to choose the correct level of a clients hair to accurately assess the right way of colouring the hair to the desired colour.
Tones are numbered from .0 to .9.
Hair colouring products can have just the base colour without any tones, or they can have up to three tones in it, though one and two tones are most commonly seen.
The first number given for the tone is the primary tone, and the second number is the secondary tone. The primary tone has more influence over the final colour than a secondary tone.