Well...that's because cameras give us the opportunity to expose the chip (CCD) or film longer, and thus capture more photons
Longer exposures allow more light and colour to be captured.
This is a very simple explanation...BTW...but that's pretty much it.
Filters, when used for visual, help bring out details...while filters used photographically help produce a composite image. So, in the case of planetary imaging, we capture a red, green, and blue image and then combine it to form a single (RGB) colour image.