There are four wires on the edge connector that represent the three colors - Red, Blue and green. There is a white wire called "sync" and maybe a separate video ground. Make sure the green wire is not loose or cut. The game will still work without the green color (as you have found out). You can also check the chassis for the GREEN color boost. All three colors are there as well.
BE VERY CAREFUL AROUND ARCADE CHASSIS - They bite.
could simply be the green adjustment potentiometer. Failing that, the green bias potentiometer on the neck board could also need adjustment - but I don't recommend that needs adjustment.
