hi - yes, even color images from OSC cameras start life as mono files. this is expected and correct.
you need to use the "Debayer" process to debayer your images.
or, if you are using BatchPreProcessing to calibrate your images, be sure to check "CFA Images".
it's a good idea to try with Debayer first because you may have to change the bayer matrix setting. if pixinsight's fits reader direction is opposite from how the fits file was written out, you may need to change from RGGB to BGGR.
rob