OpenGameArt.org
Rainbow
Credit line
"Rainbow" by Jan125 licensed CC-BY 4.0: https://opengameart.org/content/rainbow-1 Author's attribution notice: I like having a humanly readable format. Please save in .mmp instead of .mmpz or be insulted. For info, see project file.
Where to put it: Game credits or video description. If the entry has a "Copyright/Attribution Notice", follow that.