Well, the names for different parts of the color spectrum are, I suppose. Wavelength of EM radiation, and how your brain interprets it as color, is 'real'.

Light speed is constant but the apparent frequency and wavelength (which roughly corresponds to what colour we see) change due to the Doppler effect

So light is a wave. Shorter wavelengths are bluer longer wavelengths are redder. When you walk towards a wave you hit the peaks and troughs faster than had you been still. They come slower if you’re walking away from it. The Doppler effect is that but with light waves and velocities that make it relevant

Which is achieved by spacetime dilation which can in turn stretch or compress the light waves.

Adding to the other comments; I once saw a interesting video of a visual demonstration of that effect and other weird things that happen close to the speed of light. It was this one if i remember correctly: https://www.youtube.com/watch?v=ge_j31Yx_yk

For a shift from about 700nm to 350nm: coming right at you at 0.6c

It would also have a kinetic energy of about 1.1234 Petajoules, on the order of magnitude of the Tsar Bomba

I don't know about blue but here is all the math to turn a red light green.... Don't think of doing it though while you could probably get out of a ticket for running a red light I don't even know what the fine is for driving many thousand times the speed limit is.

Edit: just realized I forgot to post the actual link.... https://sciencenotes.org/fast-go-make-red-light-look-green-relativistic-doppler-effect/#:~:text=If%20we%20take%20the%20speed%20of%20light%20to,to%20convert%20to%20km%2Fhr%2C%20you%20get%20197%2C640%2C000%20km%2Fhr.

60% of lightspeed, according to another commenter.

Impossibly fast and it would have to be coming right at us.

Speed kills, coming down the mountain
Speed kills, coming down the street
Speed kills with presence of mind
Speed kills, if you know what I mean