Here is a quick fix. (although the instructions below are long and seem complicated, it only took about five or so minutes) A rough workflow is this:
Duplicate background layer.
Make a duplicate of the image. The image has an allover uniform yellow cast we want to get rid of. I am going to find a neutral color in the original image, place a layer above the image, and fill it with the opposite color of the cast. The purpose of the duplicate image is to get the opposite color of the cast, which can only be done in Lab mode. Change duplicate image to Lab mode. Select a spot on the image which you perceive should be neutral with the Eydropper tool.
Click on the color swatch to bring up the Color Picker. We are going to make changes to the Lab colors, see the L, a , and b options on the Color Picker. Select a, if it is negative, change to positive, and vice versa. Same for b. Leave L alone. Close Color Picker. The color swatch is now the oppisite color of the cast so that if you combine them, the cast will be gone.
Switch to the original image, select the layer you created above the image layer, set blending to Overlay. Fill the layer with the color from the color swatch. The cast should be almost gone if you selected the correct neutral color. The image will be darker but we will take care of that. If you are pleased with the color cast removal, merge the color fill layer and image layers. If not, try again with a different color. Trial and error and experience will let you get this right almost all the time the first try.
Now create a Curves adj. layer. Increase the lightness and contrast of the image so that it looks correct. You could use Levels, but I like curves. When correct, merge the adj. layer and image layer.
Now the sky. I am going to use a Channel mask. Look at all of the channels to see which has the most contrast between the sky and buildings. Here is a trick: you may also check the channels of the duplicate Lab mode image and see if any of them are better than what is in your original image. The channels will be different: the Lab mode color channels will be based on color only, luminosity is not included. The RGB channels, red for example, will be based on
both on color and luminosity. This subtle difference can make a difference. In some cases, the Luminosity values in the image will be close but the colors different. In RGB this may mean that there is little contrast between the mask areas. In Lab, you may find that one of the color channels has the contrast you need.
I selected the Lab b channel. It looks flat, but there is a good edge between the sky and building. Selected the b channel, Select All and Copy. Back in the original image create a new channel and with it selected, Paste. The Lab b channel is now in your original document. Use Levels to increate the contrast.
Create the masks. There are many tutorials on creating channel masks if you do not understand this process. Practice them and then come back to this project.
Not that our channel mask will have to be Inverted. The sky is black and we want it to be selected or show through, so it must be white. With our channel mask for the sky, we can work on the sky. Ctrl-Click on the sky channel mask image. You will see the marching ants. This mask has been selected. Now to place the mask on the correct layer. Back to the layer pallet, select the image
layer and click on the Add mask button at the bottom of the dialog. You now have a mask applied to your image layer. Note that the mask icon shows the sky area as white and everything else as black. This means that only the sky area will be effected when the selection is active.
The sky looks too blue and saturated for the rest of the image. I used Hue/Saturation and reduced the saturation and adjusted the hue some what till it looked more natural to me.
Almost done. I merged the image layer with any layers above it, if there are any. Then looked at the result. It still had a slight cast. So I closed the duplicate image, and made another. Then repeated the color cast removal steps above. Note that you can change the Opacity setting to vary the effect of the cast removal.
(Thanks to sample chapters from Eismann's Layer Masking book and Margulis's Lab Advantage in Layer Masking book for turning me on to this process. It is sort of a combo of things I picked up from both.
Eismann:
http://www.peachpit.com/bookstore/pr...735712794&rl=1
Margulis: (Two chapters)
http://www.ledet.com/margulis/articles.html
Larry