As soon as you’ve got the food coloring in with the sugar, screw the jar lid on and shake, shake, shake it like a Polaroid picture. It will take several seconds for the food coloring to distribute across all the sugar, and when it has, you can choose to add more color, or a second color.
The sugar can be stored right in the glass jar that you used to make it, directly on the pantry shelf for its entire shelf-life. Over time, it will stick together a little in the jar, just like brown sugar does (and for much the same reason), but a bang on the counter or a quick stir will easily un-clump it again.
To use, sprinkle the sugar directly on any iced or sticky surface. We use our colored sugar on top of cream cheese for cakes and cookies that are deliciously sweet and brightly colored but that contain no artificial colorants.