Doppler Effect.

Another path i could take the colour selection with, although there is quite a lot of information and not many visuals to take from this so i'm unsure just yet.

A blueshift is any decrease in wavelength (increase in frequency); the opposite effect is referred to as redshift. In visible light, this shifts the colour from the red end of the spectrum to the blue end. The term also applies when photons outside the visible spectrum (e.g. x-rays and radio waves) are shifted toward shorter wavelengths, as well as to shifts in the de Broglie wavelength of particles. Blueshift is most commonly caused by relative motion toward the observer, described by the Doppler effect.

In physics (especially astrophysics), redshift happens when light seen coming from an object that is moving away is proportionally increased in wavelength, or shifted to the red end of the spectrum. More generally, where an observer detects electromagnetic radiation outside the visible spectrum, "redder" amounts to a technical shorthand for "increase in electromagnetic wavelength" — which also implies lower frequency and photon energy in accord with, respectively, the wave and quantum theories of light.