What I mean is, a telescope will produce several arrays of numbers detailing the number of photons received by each sensor pixel, one array for each frequency i

What I mean is, a telescope will produce several arrays of numbers detailing the number of photons received by each sensor pixel, one array for each frequency it measures. Then you pick three arrays and pack them into a bitmap as the R G and B components. At most you can get fancy by letting it mix three artistically chosen colors (rather than red green and blue), but a lot of pictures don't even involve that. That's the same between Webb, Hubble and any other telescope. Even digital cameras do it - they differ from the human eye, not by a lot but noticeably under some conditions.