I did try to plug in to just the component slot with the green cable and got black and white video. Tested composite with green/red and green/blue and got original results of black screen with flashes of green but no glimpses of actual video from the console. I’ve also tried different games just to eliminate that as a problem. Not sure if this helps troubleshoot.
RF is essentially composite video and a mono (rarely stereo) audio stream muxed together, and composite video is basically luma (Y) muxed with color data (C, Pb+Pr); so, when you connect composite video to a device expecting luma (Y), you should get a black-and-white image. The OSSC can decode luma on its Y/G input, but it cannot decode chroma or audio, thus the black-and-white image.
YPbPr component operates by putting, effectively, a black-and-white image on one cable (luma, Y, the green one), the difference between luma and blue on the second cable, and the difference between luma and red on the third cable, leaving green to be calculated. Knowing that, it makes sense that connecting RF (or anything, really) to the either the blue (Pb) or red (Pr) inputs would get you practically nothing.
Ultimately, it shows that the Genesis is working and properly generating images; so now, either there’s something wrong with the HDRV cable and/or Genesis 1 adapter, or there’s something wrong with the composite video output on the AV jack.
Have you checked both the HDRV cable and the Genesis 1 adapter to make sure there are no bent or missing pins? You may want to track down a composite video cable simply for testing, because that will immediately show you whether or not the console is properly outputting composite video from its AV jack.