In a batter bowl or a bowl of your liking, whisk together the flour, salt, and baking powder; set aside.
In a large mixer bowl using paddle; cream the butter until it's smooth; stir in the sugars and vanilla extract until they're evenly blended.
Add the dry ingredients to the creamed mixture one third at a time, mixing well after each addition, until the dough is evenly blended.
Divide cookie dough in to 4 equal pieces. Take 2 pieces and incorporate the food coloring of choice into each piece or add cocoa to one or both pieces. Don't add both! NOTE: I will be making 1 green and 1 red piece to go with the 2 vanilla pieces.
Place each quarter piece on a large piece of plastic wrap, pat it into a 1/2-inch-thick square, and then wrap it in the plastic. Refrigerate the 4 squares until firm, about 1 to 2 hours.
Unwrap one piece of the chilled vanilla dough, leaving it on the plastic. Cover it with a second piece of plastic wrap, then roll it into a rectangle measuring about 9 by 7 inches. If the dough gets too soft and difficult to roll, slide it onto a baking sheet and refrigerate it until it's firm again, about 5 to 10 minutes. Unwrap a piece of the colored dough, cover it with another piece of plastic, and roll it into an 8- by 7-inch rectangle.
Remove the top piece of plastic wrap from both rolled doughs and invert the colored dough on top of the vanilla dough, lining up 3 sides and leaving about 1 inch of vanilla dough exposed on one side. Starting at the opposite side, lift the vanilla dough by the plastic wrap underneath it and snugly roll up both layers into a log, peeling away the plastic wrap as you go. Gently roll in sprinkles coating log. Wrap the log in the plastic and refrigerate it for at least 2 hours. Repeat the process with the 2 other pieces of dough.
Pre-heat the oven to 350 degrees. Line 2 baking sheets with parchment paper. Unwrap one of the logs and slice it into 1/4-inch-thick rounds. Arrange the slices on the parchment about 1 inch apart and bake for about 13 minutes. The cookies will still be a little soft to the touch.
NOTE: They will have a better texture if you don't allow the edges brown.
Allow cookies to cool for 1 minute on the cookie sheet; transfer to a wire rack to completely cool.