From ECWolf Wiki

TEXTCOLO is a lump that assigns color information for fonts. ECWolf has many colors predefined so in general this is not needed. This is shared code from ZDoom, so the TEXTCOLO page on the ZDoom wiki is relevant. One thing to note is the "Flat" coloring is used in game for Wolf3D 1bpp fonts. The predefined font colors may differ slightly between ECWolf and ZDoom in order to best suit already existing use cases within the engine.