Every projectile/missile is yellow. Sometimes it is hard to understand what is coming your way just by looking at these yellow dots.
That's a good idea. Friendly could be a slightly different color than unfriendly. I imagine it wouldn't be too difficult to implement. The engine already knows how to test whether a projectile is friendly or not (when it is looking at whether to impart friendly fire damage).
A lot of it is already obvious, based on the direction the projectiles are traveling, but that would mean shots from unexpected angles would stand out on the display. That might help you to notice something that you need to react to even if you don't have the unit in your vision/radar.
We should look for ways to use subtle (or bold) differences in color to convey information to players. Any time there is ambiguity about what we're seeing on the screen, we should consider whether it's possible to give cues to the user through varying colors.
E.g. have a different color for the shield bar if the shield is up or down. If the shield is down and it is recharging, showing a different color would be a simple way to communicate that.