I'm sure most of us, at some point or other, have uploaded photos
only to discover that we took a really cute photo, but that it
has a wash of color over it. The following tutorial is a quick
way to use your curves dialog box to correct that color cast.
First open the photo you wish to correct.
Click on the half black/half white circle on the layers palette
to create new fill/adjustment layer, and select Threshold. Drag
the slider all the way to the left. Your photo will be completely
white. Slowly drag the slider back until black starts to reappear,
and click OK.
Now select your Color Sampler Tool, which is located under your
eyedropper (right click on the eyedropper to see what's underneath).
Click the dropper once on the black area of your photo - this
will give you your darkest reference point. Double click on the
thumbnail of the threshold layer in your layers palette to bring
up the slider again. Slide it all the way to the right, until
your photo appears all black. Slowly slide it back towards the
left, until white begins to appear, and click OK.
With your Color Sampler Tool, click once on the white part of
your photo - this will give you your lightest reference point.
You may now drag the threshold layer to the trash can, as you
will no longer need it. At this point you should see two target
markers on your photo.
Now, go to Image>Adjustments>Curves (or Ctrl-M) to bring up the
curves dialog box. Select the shadow eyedropper on the dialog
box, (the black one) and click on the target labeled #1. This
will correct the shadows in your photo. Select the highlight eyedropper
(the white one) and click on the target labeled #2. This will
correct the highlights in your photo. If your midtones need to
be corrected, select the dropper for the midtones (the gray one)
and click on something in the photo that is medium gray (in the
example photo used here it was a portion of the eye, zoom in and
You are finished with your color sample targets, so to remove
them you go to the options bar and click the Clear button.
Below you will see the color corrected photo, with it's blue
color cast removed.