It's impossible to render the same colour online, on paper and in the flesh. Different techniques are used simply because of the medium you are viewing it on. Using light the primary colours are RGB, red, green blue to create all others using ink, look at your printer, it uses, cyan, magenta and yellow.
You will often see disclaimers on pictures online stating that the colour you see depends on how your screen/monitor is setup as this alters things as well the fact you are viewing it online and not on paper which will be different and not in the flesh, as that will appear different as well.