Determine what color your spooky sky will be, and prep your pallet or other working surface with that color and white. Using the white, paint a full moon somewhere on your paper. You will work outward from here, painting in concentric circles. Add just a touch of your other color to the white and begin to encircle your moon. Here you can get creative with your texture, using whatever brush strokes suit you and your art! This band can also be as wide or narrow as you like. Repeat, working out from the previous band. Continue to repeat this step until you have filled the paper with darker and darker gradients of your second color.