currently there is no way to change vanilla item's name color by its rarity. if we use Custom Rarity Mod to make custom rarities, item's name color will still be its vanilla rarity's color. this will make item's name color doesn't match its actual rarity, as the below image displayed:

the enchanted_book's vanilla rarity is uncommon, and its name's color is yellow, but the tooltip's frame is green. they are not matched.

therefore, i think Custom Rarity Mod needs to provide a feature to let us change item's name color (should support hex color code) by its rarity. or, just provide a way to let vanilla item's name color match Custom Rarity Mod's, not vanilla's.