I love opals, particularly Australian boulder opals. I haven’t had much luck with them though. I think I bought them too cheaply and they didn’t do well with water, becoming waterlogged.
I prefer darker opals set in yellow gold, but it’s kind of hard to know what you are getting from a photograph, and not all of them have flashes of colour.
This site has some great information on opals, opal care, and why some have flashes of colour and some don’t.
You often see ads for opal triplets or doublets, and it is not always easy to figure out what doublets and triplets are. These may help