User blog comment:JustDanceMaster2004/Just dance 2017 Menu Backgrounds/@comment-31813573-20170722174346/@comment-25225577-20170722193741

They probably have a mapping of original colors to song-specific colors.

You know how in WVC there's this horizontal bar, that has a gradient made of the same two colors as the song's menu background? That means that those two colors are hard-coded to that song somewhere in the game files.



They probably store all their backgrounds in the blue-red-yellow gradient and then convert it in the game to the song-specific gradient.