Choose Paint > Flood Fill .
The cursor becomes a paint bucket.
Click the area or color on the image layer you want to fill with paint.
In the Flood Fill Options section of the Paint Panel do the following:
Click Accept.
After Accept has been clicked, flood fill options are no longer editable until another floodfill operation is initiated. You can edit and modify the flood fill options up until you click Accept, mouse down on the image for another flood fill operation, or exit the tool.
Alternately, you can set the Flood Fill Options before clicking the area or color on the image layer you want to fill.