Hello, i have made a discord community for anybody interested in Diplomacy & Roleplaying in 0ad, I have also made a Mediterranean style map just for this you are all welcome to join and check it out. https://discord.gg/2ZT99gzd3
All German units seem to have only white shields.
Plutarch mentions them when describing the Cimbrian cavalry (but does not mean Germans only used that color).
I think Cimbrian champion cavalry could still have only white shields.
Other units could have more varied colors (or just player color)