@onceuponatime, it's beautiful, to be sure!

I spent my teen years in the south of Spain, quite close to Gibraltar... within 50 miles of where the Atlantic becomes the Mediterranean. There is a subtle difference-- at least to me-- the Mediterranean seems to almost always be "bright blue" while the Atlantic is "darker."

I'm not even sure if it's just my perceptions... or something physical like higher salinity or coastlines with far more deep cut bays and sharp peninsulas... so yeah, technically speaking a branch of the Atlantic... but then again, also very much its own.