Custom palette files are not working!

Putting a palettes (.pal) file inside /palettes folder either with the game's name or naming it 'default.pal' doesn't change anything on my end. And I've use a .pal file from the actual repository.

I've selected 'custom' inside retroarch menu but the color palette remains grey. The other options (internal, SGB, GBC, Auto...) do change the palette.