Garg is correct. Since it is RGB, the first number corresponds to Red, second number to Green and third to Blue.
A value of 0, 0, 0 means zero brightness for Red, Green and Blue. 255, 255, 255 is white because that is what you get when you mix red. blue and green light.
Violets are 0,255,0 in RGB means zero Red and Blue and full power to Green and NOT violet hence an error only a geek would spot!
The range of 0 to 255 is 256 combinations which is what 8 bits gives you, 2 to the power 8. Three 8 bit values gives you 16 million colours possibilities.