Back in 1976 or so, the model makers at ILM created a number of studio scale models to film the Death Star trench sequences. There were at least three X-Wings, one of which is knows as the Red 2 model because it represented Wedge Antilles with the call sign "Red 2."
The astro droid used for this model is actually different than the prop used in the live action filming. In the scenes filmed with the actor, it seems that they recycled an all red dome that can be seen in Mos Eisley. This dome be viewed over the actor's right shoulder for a few seconds.
For the actual model, ILM painted a red/silver astromech. It makes perfect sense: red does not interfere with compositing and is easily separated from R2-D2's distinctive blue dome. Luckily, Wedge was one of the few pilots to survive the battle, and so did his Red R2!
For more images of the Red 2 model, and tons of great resource photos of other Star Wars and Sci-Fi craft, please visit the great folks at StarShipModeler.com.