Here’s a cheerful rainbow ring tutorial(here’s the English translation). The author even mentions it’ll lighten up your mood. The body of the ring is made from a rainbow stack. You could do this as a blend but even the stack of discreet colours looks pretty good here.
Later in the tutorial when the maker goes to add the second part, the bump, she questions why she didn’t just form that from the original cut but this was a first try and it looked pretty good. The ring seems to be baked once the rough shape is made and a drum sanding bit is used on a rotary tool to take the rough bits out.