Had a mix of Hickory and some maple ( MM- from 16 to 18%) got good fire going, probably the best I have had in awhile. Stove cruising at about 520 for quite awhile, flue temp (single wall) about 285. Got busy doing some stuff and when I checked this is what I saw. Secondary still burning a lot, lots of coals. Some blue, yellow and some orange flames in the wood. Wondered what could cause this dark brown just in this corner. Never had it before. Will do the dollar bill test later when stove is a bit cooler. I had done it a few weeks ago and it was fine.