Using the healing brush

Select the Healing Brush tool from your pallette. Now select the correctly colored area on the picture (Option + Click) and using the healing brush use your mouse to touch up the photo. Be aware that you can change your brush size and the hardness of the brush. The brush hardness defaults to 100 which means a very crisp edge, blending in photo editing is VERY important so I always set my hardness to 70% and then adjust from there.

Source: Beyond Megapixels