After selecting the Bucket Fill tool in the toolbox, click the Pattern Fill radio button, and then click the thumbnail pattern that appears to select one of the available patterns.

You can also use the Bucket Fill Tool, located in the main toolbox, to fill your workbook with color. Once you select the tool, choose within the toolbox settings and set the Fill Type to the ...

Once youv'e made an outline, navigate to Select>From Path, or hold Shift+V to activate your selection, then use the Bucket Fill Tool or Paintbrush to completely fill in the selection with white.

Duplicate the layer (Layer>Duplicate Layer) one time for each color you want to use, then use the Paintbrush or Bucket Fill tool to make the image a different color in each layer.