Pinkie Pie recalls her days on the dreary rock farm, when color was muted and bleak. Her first real sighting of how bright and cheerful colors could be came from the sonic rainboom Rainbow Dash caused.
Now, Pinkie Pie wants a new color. The current ones just aren't enough, and they don't do enough to make ponies happy for long periods of time. She wants something unique and exciting, and so she talks to her friends in her quest for just such a thing.