What are X-rays?

Answer 1

You can't see X-rays, so we don't really have a name for their "color" other than saying they're "X-ray colored".

You might be asking how one could create a color X-ray. One way would be to choose three different wavelengths within the X-ray band and assign each a different color that we CAN see (red, green, and blue) and then combine the image at each wavelength to form a composite color image. This sort of thing is done in Astronomy all the time (with various spectral ranges being reassigned to visual; often the wavelengths chosen correspond to lines in the spectra of particular species).

Answer 2

X-raysX-rays are very penetrating EM (Electromagnetic) radiation, by definition x-rays are produced by electrons being suddenly stopped or given a sudden change in direction at higher energies. They are higher in the spectrum than ultraviolet and typically but not always lower than Gamma radiation.

A medical x-ray uses a small carefully controlled x-ray source to get images of the inside of living things (people, dogs, cats etc). Industrial x-rays are typically used to verify the quality and internal structure of manufactured or welded items.

The energy level and frequency of x-rays can overlap with gamma radiation, the definition of gamma radiation is EM radiation that is emitted by the nucleus of atoms. Typically however gamma radiation is much more energetic (higher frequency), more penetrating, and dangerous. Gamma radiation is also much harder to produce artificially.