Any color of wool is fine. Currently, the shade of the wool has no influence over the resulting painting.
Place the wool in the center slot. Place the 8 sticks in all of the remaining slots.
Paintings can only be placed on flat vertical surfaces.
Mark the bounds using any solid block. Place the painting in the lower left corner. Expect the painting to expand to the top right corner, to try to fill the space.
Paintings placed facing north/south are brighter. Paintings placed facing east/west are darker.