How To: Remove pink areas from HDR
Pink patches in HDR images are caused by overexposed areas in your source photos. When most or all of your source images are too bright (overexposed), your HDR software (such as Photomatix) has troubles processing the information, and oversaturates the areas.
Fortunately, removing these pink areas are easy with a little planning, and / or a little photoshop.
The best solution is to shoot more frames at a wider range of exposures. If you ensure you have at least one photo that is not overexposed, you'll have a better resulting image. For some situations, it's as easy as bumping up your shutter speed. In others, it may involve a higher aperture.
You can get a better idea of which parts of your photo are over or underexposed, by turning on highlight warnings on your camera. On my EOS 40D it's called "Highlight Alert". When I take a photo that is too bright, the overexposed areas show up as black blinking spots, marked in red in the image below:
If you've already taken your shots and need to remove pink overexposed areas, you can do this using Photoshop's Colour Replacement Tool.
To use this tool, open your image in Photoshop. Press and hold on the brush icon to bring up the list of additional tools, and pick the colour replacement tool
To use the tool, set the colour you wish to REPLACE as the background colour, and set the colour you wish to replace it with, as the foreground. To get the colour of the pink, hold down ALT and click on the pink area.
In the settings, set "Limits" to "Discontiguous", "Tolerance" to 30%, "Sampling" mode to "Background swatch" and "Mode" to "Colour".
Now you can simply paint over the affected areas. You may need to select the colour more than once, as there might be various shades of pink.