option window, set Background style to Current Brush Color, Black, White or Transparent.Select a canvas (make it active).
Choose Windows > Editors > Canvas Layer Editor
to see the layers on the canvas.
Click on the Background layer to make it active.
Choose Paint > Flood Fill
from the palette.
Choose a background color from the Flood Fill Options in the Paint Control Panel.
Click on the canvas in the view to apply the paint.
Remember to select a different layer in the Canvas Layer Editor before you start sketching.