The pairs of LEDs can be single bicolor LEDs that have back-to-back chips inside the package. You only need one mounting hole, and there are fewer wire leads to connect.
The downside is that color blind folks may not be able to distinguish the colors, but they could tell which of two separate LEDs is lit. (Same problem with traffic signals. That is why you don't see a single source that changes colors from red to yellow to green.)
