This patch colors Zero's forehead gem on his sprite to be blue (instead of gray) using the 2 color slots normally for the buster (which is filled in with colors from his body) and modifies the palettes to match.
Made using TileMolester, CrystalTile2, and GBA Graphics Editor.
Examples of the hack with custom recolors: https://imgur.com/a/fb0p5MQ
Make your own recolor codes: https://gamedj.github.io/gba-mmz-sprite-recolor-guide
Database match: Mega Man Zero 2 (USA)
Database: No-Intro: Game Boy Advance (v. 20180816-092117)
File/ROM SHA-1: C4D93A58F0F82C526DEC8A3FDBDA170336303689
File/ROM CRC32: CE1E37BB