The GBC assigns color palettes to certain monochrome Game Boy games, In this hack the palette was assing to the default colors
Metroid II - Return of Samus (World).gb
CRC32: DEE05370
MD5: 9639948AD274FA15281F549E5F9C4D87
SHA-1: 74A2FAD86B9A4C013149B1E214BC4600EFB1066D
SHA-256: 3080BCC2EB9965DE463F5F4E02F0DABBB13B060E1654A18DA8B50948C10AF4A6