What regions do Red Beacons/Supply Caches usually appear in

The location of the beacons is fixed and each position has a range of colors the beacon can be. Not all colors are possible everywhere, see this map for the possible colors at each location. Higher quality drops are rarer than lower quality drops, though, so a location with a red-mark does mostly spawn non-red drops. Some drops also trigger the spawning of creatures like a rex in the area.