It depends on what you are trying to do, but in general you would be dealing with some variation of RGB colour coding.
0 means some minimum (e.g. none) value for that colour, and 255 (or 0xFF, in hexadecimal) means some maximum value for that colour.
Since white is the combination of all the colours, it can be seen as the maximum of all the colours, so white is (255, 255, 255), or perhaps 0xFFFFFF