<canvas

  width="400"

  height="400"

  canvas_background="NONE"

  color_mode="HSB"

  paint_hue="0"

>

  <paint-bucket show="IF, first_frame" c="'black'"></paint-bucket>

  <circle

    show="IF, mouse_dragging"

    anchor="mouse_pos"

    stroke_color="NONE"

    fill_color="paint_hue, 100, 100"

    paint_hue="(paint_hue + 1) % 360"

  ></circle>

</canvas>

​