I think the only thing you need to do to get the tails back on your contacts without adding the different colors as well, is to replace the GWX ContLine.tga file with the one from the stock game (or from the Contact Color mod, if you don't have a stock installation to copy files from).
Based on the mod mentioned above for GWX2, I removed everything from GWX3 Contact Color except the ContLine.tga file, and went into the game to see - I had the tails back on the map but all contacts were grey.
Granted I think I only went into one of the academy tutorials, but I'm sure I tried that before with different permutations of Contact Color and still had colored contacts (even if they were all neutral green). Replacing ContLine.tga and nothing else put back the tails but not the color so I'm pretty sure that does the trick.
If it turns out it doesn't work as planned once I'm out on patrol, I'm sure I'll be back asking about it again.
