Scientists put a lot of thought into the design of instruments to send on spacecraft to explore other worlds, they can't change anything once the spacecraft is launched so they need to maximize the science return from their payload where mass limits are critical.
Despite colour cameras being the norm with consumer hardware, there's technical advantages to using completely different technologies for taking images in deep space. Instead of using off the shelf colour cameras the preference is for monochrome image sensors with filter wheels that can be switched through to take multi colour images through a slower, more accurate process.