Board Thread:New on Pretty Cure Wiki/@comment-25034020-20180107030112/@comment-31119526-20180114094631

People speculate about the colors of potential new Cures every year. This year the ideas are purple, based on the tambourine having a part with that color, and green, based on one of the stars on the Melody Sword. Unless one of these toys includes more than just some random color though it's just speculation.

There have been toys that play transformation phrases and such. That would be more useful evidence. IIRC Cures Scarlet and Felice were discovered that way before they were officially introduced.