The only postproc is the ffmpeg step to package the raw h.264 stream into something playable… or shovel the output off to youtube for a livestream.
However, I got the problem solved. Note that the raspistill command didn’t have the -hf and -vf switches as the raspivid command did. Not sure where I saw to use those on raspivid, but those were the culprit. Take those switches off, and the colors look spot on right.