Hi guys,
in the past weeks I have been collecting information on WWII-era puffers. I have identified 78 private-owned 20-m puffers and I managed to find funnel colors and house flag used by some of their owners. I would like to add those features, but before I do that I would like to hear from the most knowledgeables on naval history among you (Sailorsteve, Iambecomelife, are you there?

).
My doubts are:
I know military vessels and ships which sailed in convoys were painted either light grey or with camouflage patterns, but what about small coastal vessels? Were they repainted in plain color as the war approached, or they retained their original paint schemes?
From the little information I have, house flags could be hoisted on the main mast but apparently their usage is not subject to any strict regulation. My question is: how commonly they are used and how realistic would have been for a vessel to fly one in wartime, when it vivid colors could have unnecessarily given up own position to the enemy?