This ring from Coup de Coeur speaks to the kid inside, with its chunky rainbow stone. I should say mystery stone, as there is no detail on the site as to its composition. Ditto the setting, as all it says is gold plated but there are references elsewhere to using sterling silver, so it could be vermeil?

This sells for £120, and is available in a plain gold or silver colour as well, should rainbows not be your thing.