This is because light travels faster than electricity. What people describe as "rainbow puke' is actually the photonic representation of what you would hear in the old dial-up connections—just with orders of magnitude more data. When you use multiple colors, you are broadening the spectrum of light. Since more wavelengths are available, you are actually inceasing the bandwidth of the data stream.

Of course, light does not travel in a continuous stream of a particular wavelength, but rather in RGB packets called quanta. "Quanta", being the plural of "quantum" and when used in computers is where we get the term "quantum computing".

So, while you pay a little extra for RGB, know that with it you'll have your very own quantum computer!