Photographs are a lot like Dungeons and Dragons minis. They are great for determining party order, but as soon as they go on the table you are laming out. It's a game of the imagination, dude, you should be using that time to think rather than laboring away at Hardee's so you can afford a bugbear raiding party for the next game.
So imagine a Slurpee cup full of root beer Slurpee. Got it? Now roll for surprise.
Anyways, I have no picture for the 7-11 root beer Slurpee. I could, if I so choose, use any one of the scads of Coca Cola Slurpee photos I have pinned up around my boudoir. The Coke and root beer are visually identical. However, I choose NOT to share my pornography on the internet, so you get no picture, real or fake.
Root beer Slurpee is perfectly acceptable if you like fake root beer. I think it's a branded root beer flavor, I can't remember, but either way it's a generic chemical candy root beer flavor. No goodness or reality about it, just the signifier for root beer. So, yeah, you can drink the stuff. It's cold, and it doesn't taste BAD.
And that is pretty key. It doesn't taste bad. There are two different sorts of Slurpees in the world, the "soda" flavored and the fruit flavored. Cherry Slurpee? Awful. Tastes like gross candy and corn syrup. Coke/Mountain Dew Slurpee? Not bad, not bad at all. The root beer falls in the "cola" side of the issue.
So yeah, it's okay. Get Coke, though, it's better.