Blaze Powder is a material added by vanilla Minecraft. It can be obtained by processing Blaze Rods. However, it can also be created by infusing Glowstone Dust with Destabilized Redstone using a Fluid Transposer.
Thermal Foundation changes the texture of Blaze Powder to match better with those of the three other elemental powders added by the mod: Blizz Powder, Blitz Powder and Basalz Powder. This can be undone in the mod's configuration file.
In the CoFH mods, Blaze Powder has several uses. First of all, it is a critical ingredient for creating Pyrotheum Dust, and, ultimately, Blazing Pyrotheum. It can also be used to craft Obsidian Rods. Lastly, it can be used to craft Magmatic Florbs.