When Taylor Swift sang, 'Shake it Off!', in 2014 she was not likely referring to the new battle inside fast casual dining: The battle of the most colorful and peculiar frozen beverages. The mega-pop star may have been more prescient than we know because Starbucks and Burger King have released rainbow colored frozen concoctions that are guaranteed to give you a brain freeze while adding heaps of calories by the sip.

For Starbucks (SBUX) it's the Unicorn Frappuccino, which it describes as a "...blended creme made with a sweet dusting of pink powder, blended into a creme Frappuccino with mango syrup and layered with a pleasantly sour blue drizzle. It is finished with a vanilla whipped cream and a sprinkle of sweet pink and sour blue powder topping." The actual components of the pink powder and pleasantly sour blue drizzle are still under investigation and may not be completed during the limited release of the drink in North America from April 19-23. The 5-day window of sales for the $4.75 rarity packing 470 calories only adds to the mystery of this Unicorn, which according to Starbucks, "Is only available if you believe."

(See also: Starbucks to Provide 100 Million Healthy Coffee Trees By 2025)

Photo credit: Burger King

Burger King must believe a market for rainbow frozen beverages is really a thing, because the Home of the Whopper is all in with its Fruit Loops Shake. Burger King, part of Restaurant Brands International (QSR), describes this breakfast/dessert crossover as a, "Velvety Vanilla flavored soft serve with Froot Loops cereal pieces and sweet sauce spun to perfection to create our twist on one of America's classic breakfast cereals." Burger King has teamed with Kellogg's (K) to create this piece of caloric synergy, which packs 720 calories, 103 grams of sugar and 11 grams of saturated fat. Our investigators are still looking into the source of the, 'sweet sauce', that is spun to perfection, as well as the price point, which the company does not list on its website. (See also: Burger King Diversifies Menu with "Whopperito" (QSR))

American ingenuity never surprises us, and Burger King has done its best to up the ante lately. It's 'Chicken Fries', and 'Mac & Cheetos', inventions demonstrate clearly that the Home of the Whopper is not playing around. Shares of its parent, Restaurant Brands International are up 40% in the past year. Starbucks shares are down about 3% in the past year. But if you believe that these mystery rainbow frozen calorie bombs are going to impact stock performance, I have a Unicorn for you to drink.

Want to learn how to invest?

Get a free 10 week email series that will teach you how to start investing.

Delivered twice a week, straight to your inbox.