Get at least 5 pieces of black poster board for two average windows. Measure twice, cut once! Measure the size of your windows, we were just in luck and the poster board fit top to bottom in each pane, but not the width. We had to cut the 5th poster board to make up the difference for each of the 4 "panes."
Use a plate or something of the like for a template and cut black circles out of the piece that you've cut from the triangle as pictured.
Use yellow and orange tissue paper to cover the cut out triangle (I put yellow down first, then orange behind it to make it a dark yellow).