Here we see the blue axis of the color cube, which ranges in value from 0 (pure Black) to 255 (pure Blue).

Numeric values for colors are often specified in hexadecimal (base 16) format, because it relates more closely to the way computers store numbers internally. In hexadecimal, each column is a power of 16, and the numbers 0–9 are extended with the letters A–F to enable counting to 15 with a single digit. So, for example, the number 42 would be represented as 2A (2×16 + 10), and 255 is represented as FF (15×16 + 15).

Color depth refers to the number of bits used to store one color; the greater the color depth, the more different colors a system can display. 24–bit color is widely used because it produces a range of over 16 million colors, approaching the limits of human perception. It is also popular because it conveniently allocates 1 byte (8 bits) for each color. A byte can represent 256 (2 to the 8th power) unique values, from 0 to 255.