Coincidentally I do know someone who designs flags! How weird is that?
I did actually begin work on ECW flags in 2012 and posted one Royalist infantry set here: https://nba-sywtemplates.blogspot.com/2 ... alist.html Although I did continue to experiment on and off (I recently created a flag of Allan Apsley's Regiment for someone) I have not really been very diligent at it, partly because there did not seem to be much interest, and also because the SYW and latterly the WSS have eaten up a lot of time and energy. If there are specific ECW regiments whose flags you'd like, let me know and I'll see what I can do.
One odd thing I found about ECW flags is that the gyronny style (flags divided into segments to indicate the seniority of the company commander - eg Charles Gerrard's Foot) was unique to the Royalists.
Kein Plan überlebt den ersten Kontakt mit den Würfeln. (No plan survives the first contact with the dice.) Baron Mannshed von Wreckedoften, First Sea Lord of the Bavarian Admiralty.
BTW flag-wise for the ECW, I have acquired nearly all I need.
This often meant I'd name a unit not because of an OOB, or because I liked it but because I could get the correct flag.
One exception was Covenanter dragoon flags. My 2 units don't, & probably won't, have a flag.
Tillier's Regiment. Sources indicate a Green flag. I found a green flag.
Sources say green coats for "Irish" regiments - although mostly English & Welshmen, they were in Ireland at the start of the civil war. So green coat. Lining? No hint but usually white. I gave this lot red, in homage to the 60th Rifles.