There have been many satellites used to observe X-rays. Two of the best that we have today are the Chandra X-Ray Observatory and RXTE.

Chandra is able to produce images of X-ray emitting celestial bodies. Scientists then assign a color to each position based on the spectral data.

RXTE does not produce images; instead it collects its data as a time series of counts and energy versus time. Therefore, RXTE produces data which is analyzed using light curves (intensity versus time) and spectra (intensity versus energy).