We believed this photo would benefit from a bluer sky.
Instructions
1) First, we took this image to Fast Fix, which is the best starting place for an underexposed photo.
2) Next, we moved to color and clicked the white, highlights button on the Tone Range tool, because the sky in this photo fell into the lighter tones. This automatically masked all areas of the photo except for the lighter areas.
3) We then moved our cursor on the color caster toward blue until we achieved the sky color we wanted. These color changes also affected other light tones in the photos and gave them a blue cast.
4) We then chose remove effects in the brush and mask area, used our brush strength at 100% opacity, with a brush size in the medium range, and simply brushed away the blue in the Taj Mahal.