If you are running the external LEDs parallel to the existing LEDs on the board, that is the problem. If not, you can ignore the rest of this.
If the Green-Green pair are not very closely matched, all or most of the current goes to one LED leaving the other one dim or off. Same thing for the Red-Red pair, although in your case they may be matched closely enough. If this is what you are doing, the solution is to disconnect the LEDs on the board. You could install the Green-Green pair in series, but then you may need to find and reduce the dropping resistor on the board. This makes your task a bit more complex.
I have run LEDs from the same lot in parallel against conventional wisdom. Some play well together and some do not. I have even had pairs that shared current well for a while, then later one steals all the current. Best practice is to run LEDs in series, not parallel.
Bob
