I'm kind of wondering if you might keep looking, and find some options that are not just black or white, for the reasons already given (see-through white, heat-trapping black). Although one of my favorite beach coverups is black. It's just a little simple black bamboo knit dress with a v-neck top, and subtle drawstring at the empire waist (which I keep very loose for ease of pulling over my head to put it on), and a very slightly flared skirt that hits at the knee. It's about five years old so it's getting a little faded, but it's perfect for when I want something I'm not worried about messing up. I think I found it at Marshall's or TJMaxx. It looks a lot like this one:
http://athleta.gap.com/browse/.....=584853002
They have some cute options on the Athleta site as well.
I have also started wearing my Rachel Pally sleeveless knee-length caftan dress as a coverup, especially when i go on vacation and want to travel light, with pieces that do double-duty. I did a quick search and didnt find my dress, but I found this, which I think would look awesome on you, although I admit her stuff is expensive.
http://www.amazon.com/Rachel-P.....38;sr=1-41
This is not to say there is anything wrong with the ones you posted! I just thought I'd make it even more difficult and throw some other options at you.