If you don't get a good photo, you might be able to tell what's missing by tracing the wiring on the back. I bet the switches of the same color are all wired together in parallel. The roto target doesn't really know what position it's in so one green target probably ends up looking like the next as far as the circuit is concerned.
If you can trace from a missing target to a target that's still there that's probably the missing color. You could probably trace wires or use your multimeter to test the contact points on the front. Beware that they may all share the same common wire so you'd want to check or trace both contacts for each switch.