@brentriddell to apply it first put the file tweakvec.py into directory home/pi/tweakvec/ on your sd card ( or other storage whre retopie is installed if that).
Then you can enter in terminal window on your PC or in retropie console next:
But after next reboot you got standard ntsc mode ( with wrong colores), so if you want tweakwec fix always turned on you need write this command in file /opt/retropie/configs/all/autostart.sh It will be run tweakwec automatilly at every retropie start.
But in the end i've get right colors but also get "flickering" in some games. So to get flickering off i've used progressive mode ( write sdtv mode = 16 in config.txt)
Maybe it was helpfully too ( find my messages in the bottom of thread) https://github.com/raspberrypi/firmware/issues/811manekinekodesu created this issue in raspberrypi/firmware open Support for progressive PAL60 in config.txt/sdtv_mode #811