CBSE Class 12-science Answered

Only electromagnetic waves with wavelengths from 380 nm to 780 nm have colours that human eye can recognize. It's called visible spectrum. The electron wavelength is outside visible spectrum, hence no question of labeling it a colour. That would be same as asking what's the colour of radio waves? 

It's just energy, it's all to it. When particles move at speeds comparable to the speed of light or to the value 3x10⁸ m/s, kinetic energy is no longer given by mv²/2, and photon's rest mass is zero,  it has no substructure, it's the elementary particle, so no question of internal energy. It might be appropriate to call it kinetic energy, if required.

Yes, law of conservation of momentum hold good. The free electron are in a continuous state of random motion.

Regards,

Team,

TopperLearning.