Helmet Plumes?

[Victrix]

These illustrations may be of help. The first is from ”Kriegskunst zu Pferd” (1634) by Johann Wallhausen. The second is from Osprey Men-at-Arms series ”Imperial Armies of the Thirty Years’ War” (2010).

I think the Imperial side in the 30 year war generally initially wore white field signs, whilst Wallenstein ordered red field signs in 1632. Sweden I think usually wore yellow field signs towards the end of that war. Not sure the field sign colour was used in helmet plumes also or only for neck scarves and sashes. A red ostrich plume would look quite dramatic.