I've just made a tiny LW2 mod (with the help of amineri, thanks to her) that switches the color of all the new Advent units (but not the new alien types) to the classic black/while/red colors used by vanilla XCOM 2.
Here's how it looks:
I did this because I visually prefer the totalitarian police state aesthetic instead of looking at a rainbow of colors, which I recognize is useful to recognize the new units but it is not absolutely necessary, IMHO, since in many cases the colors really stand out against the background.
The list of changes is:
* Gunners, Engineer/Grenadiers and Sentry/Guardian/Sentinel are now black
* Rocketeers are white and they now use the Lancer helmet
* Both Sergeants are red
* MEC Archer and Longbow are black
* Scout is black and use the Lancer helmet
* Commando and Shock Troop are white, Vanguard is black
To try it, download the zipped file, make a backup copy of LW's Config folder (usually located at C:\Program Files (x86)\Steam\steamapps\workshop\content\268500\844674609) and extract the contents of the zip file to the \Config folder, replacing the XComLW_AlienVariations.ini