So, all the RPG's are put into groups of three. The first RPG in each group plays during the red months. The second RPG's play during blue. The third play during green.
Notice that group 3 only has two RPGs. That's the beauty of this system. If another game pops up, it would be RPG number 9, get put into group 3, and play on green months. If yet another games starts, we just create a new group (Group 4), and it becomes the first RPG in that group, playing on red months.
What this method does is ensure that no month has more than two sets of RPG's running at a time. So, if we were to put the big three (DC, Marvel, OU) into Group 1, everyone playing in all three of those games would only ever have to worry about playing two sets of characters at a time.