This drink consists of mango syrup in a pink creme Frappuccino base, sour blue drizzle, whipped cream, and sour pink and blue powder on top. The "Color-changing" aspect in the advertisements likely comes from stirring the blue drizzle through the pink base, making the drink purple later on.
Or, if you leave it alone without mixing it that well, it starts to turn into something like a Lush bath bomb inside of a cup, haha.
After reading a number of reviews online, it seems like there's some inconsistencies with the sweet/sour aspect of the drink. Many people said the drink was too sour, while other said it tasted like a funky colored vanilla Frappuccino with no distinct fruit flavors. For me personally, I got a lot of mango flavor throughout, which reminded me of a mango Rita's water ice (so good!!) at first. Then I did get a few hits of sour flavors, I think from when I finally started drinking the blue drizzle along the side of the cup. The powder on top was pretty sour, but nothing more than maybe a bite of a Sour Patch Kid gummy. But as expected the predominant flavor was very, very, very, sweet. I got about halfway through the drink before deciding that it was something fun to try but I did not have to finish, haha. I can definitely say I'm happy I tried it, especially since I used a drink reward for it so I didn't technically pay up front for it anyway.
As a side note - I have to laugh at the Starbucks Facebook page comments (seriously, go look), with all the people blasting Starbucks for making a drink too sweet and unhealthy. Last I checked, NO ONE is buying this for health reasons, and people can choose to not get this drink (or any drink/food for that matter) if they don't want to. When it comes down to it it's a fun and crazy drink, and I hope they keep coming out with more fun flavors moving forward!