In computing, especially when using HTML, one tends to use RGB color codes. They appear as a string of six hexadecimal digits.
The first two digits represent the intensity of red light, the middle two digits represent the intensity of green light, and the final two digits represent the strength of blue light.
The values range from 00 (zero intensity) to FF (full intensity). In a "256-color" (really a 216 color) system, the only legal intensity values are:
• 00 (zero intensity)
• 33 (20% intensity)
• 66 (40% intensity)
• 99 (60% intensity)
• CC (80% intensity)
• FF (full intensity)

In a "24-bit color" system, any possible hexadecimal integer from 00 to FF may be used, making roughly 16 million possible colors. Most of these are so similar to other colors that you may not be able to tell them apart by eye, earning it the name "True Color".

Example: FF8000
FF at beginning = full-intensity red
80 in middle = half-intensity green
00 at end = zero blue
Since red + green = yellow, and this color's green is only half-intensity, you know that this color is halfway between red and yellow, i.e. orange.