From 《三国演义》 Chapter 25, where Cao Cao looks down at Yan Liang's army drawn up with 「旗帜鲜明，枪刀森布」 — banners bright, weapons bristling. Originally described a neat military formation; the modern sense transfers to ideological clarity.
usage
Now almost exclusively about taking a clear ideological or moral stance. Very common in political writing, especially when demanding that someone 'show their colors.' Usually modifies 反对 (oppose) or 支持 (support).
