I just finished building my OSSC and flashing the initial firmware and it does work except for the red channel.
It seems like red is always at the maximum value. This happens with both the SCART and the VGA input.
When I lightly touch the PCB between U2 and U1 with my finger, the image partially changes, but the areas that changed look like red is 0.
Assuming that test pattern displays correctly, you either have some high bit(s) of R-channel bus between TVP7002 and FPGA floating, one of the TVP7002 P/G pins near R_IN* disconnected, or damaged TVP7002.