Use the Paint Bucket tool
The
Paint Bucket tool 
fills
an area that is similar in color value to the pixels you click.
You can fill an area with the foreground color or a pattern.
-
Set options in the options bar, as desired, and then
click the part of the image you want to fill.
If you don’t want to fill transparent areas
in a layer, you can lock the layer’s transparency in the Layers
palette. You can specify any of the following Paint Bucket tool options:
- Pattern
- Sets a pattern to use as the fill.
- Mode
- Specifies how the paint that you apply blends with the existing pixels in the image.
- Opacity
- Sets the opacity of the paint you apply. A low opacity setting allows pixels under a paint stroke to show through. Drag the pop‑up slider or enter an opacity value.
- Tolerance
- Defines how similar in color filled pixels must be. A low tolerance fills pixels with color values very similar to the pixel you click. A high tolerance fills pixels that have a broader range of colors.
- Anti‑alias
- Smooths the edges of the filled selection.
- Contiguous
- Fills similarly colored pixels that are next to each other. Deselect this option to fill all similar pixels in the image, including those that aren’t touching. The Tolerance option defines how similar the colors must be.
- All Layers
- Fills similar pixels on any visible layer that are within the levels set by the Tolerance and Contiguous options.