Before you start painting, you need to choose the color that you want to apply to your photo. In the color palette at the very bottom of the toolbar, click the foreground color swatch (which is the one on the upper left). You should see the Select Foreground Color dialog, where you can browse for and mix colors until you get the exact shade you want. When you are happy with the color, click OK, and you should see the swatch in the toolbar change accordingly.

Now start painting. Click in the photo where you want to change the color, and you should see the old color replaced by the new color. Now just paint to apply the color. , you can see I've begun changing my daughter's dress from green to purple. (Note that I just painted over the white pattern; the tool's tolerance adjustment lets it ignore huge differences in contrast.)

Depending upon the way the tool was configured, you might run into some easily correctable snags. For starters, the brush might be too large or too small for the area you are trying to paint. I generally pick a brush that's about a quarter the size of the area I'm working on. To do that, click the Brush drop-down in the Tool Palette at the top of the screen and set the brush size in pixels. Make a first pass on the photo to do most of the work, being careful not to color outside the lines; we'll fine-tune the edges later.

Another setting you'll want to tweak is the Tolerance control. Tolerance determines how similar the nearby colors have to be in order for the Color Replacement tool to paint over them. If the tolerance is too low, the old color won't get satisfactorily replaced; too high, and you'll end up including dissimilar colors you didn't want. I recommend setting Tolerance (also found in the Tool Palette) between 30 and 40 percent, and experimenting from there if that doesn't work for you.