I would have to choose the sky. For starters it’s the biggest visible item, so it would maximize the amount of color that we could all see. The main reason is because of the shear prism of colors that the sky projects. So we would not be stuck with just one color and countless shades of gray. Instead we would have blues, purples, yellows, and a couple others. I’m not sure if the rules would allow the coloration of just the sky itself, but imagine how great it would be if it included every thing that is in the sky and is therefore part of it. Another DP participant said the ocean, problem is that the ocean derives its color from the sky’s reflection. With no color in the sky there would effectively be no color in the ocean.