“A strange, entrancingly beautiful looking golden ring, the adorned gem seems to refract light through it in every color of the spectrum.”
When fishing in the dark sea, around layers 2-3, you have a small chance to fish up this ring.
On use, your character puts it on, and it adds a permanent effect to your info menu. Similar to your dodge reflex.
This effect lets you change the color of your magic to any existing color of the same magic. Say you have red plasma, but preferred purple, or hot air but preferred base.
This would obviously also change the move names to their respective (red to purple, ruby to citrine, etc)
Lorewise, this is just a quartz ring a sailor was wearing before perishing in the dark sea, and due to the extreme magic pollution in the water, it gained prism-like properties over the years under the sea, which when channeling magic through it, can change the color without inherently changing the magic itself.
(And as another addon, there’s a setting for it to change every weapon color to be either random or a specific color)