Hey there. I'm a case junkie and a bit of a collector too, so maybe I can help you out a bit.
I have the jet black phone though, so maybe not.
But here's a clear insight of Ocean Blue on the Matte Black. It is a beautiful colour. It's actually still my favourite.
Unfortunately I don't think you'll get very far - Ocean Blue and Sea Blue have been discontinued/removed from sale with Apple (making them extremely hard to find), while Azure can only be ordered online + shipped, making it more effort than it might be worth. In Europe (there on holiday now), Pebble has already been discontinued. Since the 7 came out, Apple moved to a seasonal, limited time edition model (like the Watch bands) with their phone cases - get them in a colour while they're still in season and available or miss out, I know, it sucks.
All the best though - you can still try eBay and possibly a third party retailer, but then you won't get the generous 14 day return policy.