I'm not adding new features etc. to this mod, I'll only touch it if something breaks it entirely. I'm not here to provide additional plater support, the mod works and everything you need to know is written below, if it still doesn't work then you did something wrong I don't want to investigate into.
Changes color of your longest active brand, you can select a different color in options.
Play around with priority setting if you have other mods also doing coloring. (actually read the mouseover tooltip to understand how it works)
You need to be tracking your Fiery Brand under the regular debuff buff-frame. If it isn't displayed there or for example you only display it through special auras then the aura will not be able to get the information.
You can try replacing code to "BuffFrame2" from just "BuffFrame" but that's not guranteed to work for you.
Testing the mod on dummies will have weird results, test it in dungeon / open world mobs