Instructions:
Press 1, 2, 3 to pick a color (red, green, blue) and draw with mouse. Press arrow keys to movess. Press "S" to toggle drawing mode between "squares" and "slanted" (initially "squares"). In "squares" mode, a pixel's color shows the colors that appear in equal amounts on the left and on the right. In "slanted" mode, a pixel's color shows the colors which have at least as much mass on the right as on the left. Recall that red + green = yellow.