Option of Color based on laser Damage.

TLDR:
Lasers could start red, and as it's damage increases with research, it should start changing colors, finally ending on Blue after some threshold.

Details:
As you probably already know, in real life the color of the light indicates the energy density of a laser beam. The total energy obviously depends for how long a laser shines at a target and the intensity of the light. But given those parameters are fixed, it's is color (determined by the light wavelenght) that indicates the energy of the light quanta, the photon.

Changing color of lasers in real life is actually more complicated, the amplification system to make a laser requires specific materials that will generate light at a specific wavelength. Red is the simplest one, green is easy as well. Blue laser equipment tend to be more bulkier.

If you want to increase a laser "damage" you can simply, increase it's intensity, which is the obvious approach and how we can reason of "how could it work on Factorio". When you research laser damage, you just get more powerful laser due to high intensity (more light per second). That should make the laser brighter though, and also requires more energy per shot.

Another approach to increase laser damage could have been decrease the laser light wavelength, bellow a list of the colors of light for each wavelength, the smaller the wavelength the higher the energy:

Blue: 450–495 nm - highest energy, more damage
Green: 495–570 nm.
Yellow: 570–590 nm.
Orange: 590–620 nm.
Red: 620–750 nm - lowest damage

If you imagine this as a spectrum (as it is), each laser damage research could change the laser color to the next level. After some threshold, it becomes blue.

I think if you add this as a mod option, it would just be reaaally fun.

I hope that finds you well, bro, as a physicist I just couldn't keep this to myself .