HERE’S A NEAT TRICK FOR IDENTIFYING AND CORRECTING COLOUR CASTS IN PHOTOSHOP...

It’s best to fix colour casts in a raw converter like Camera Raw or Lightroom before bringing the image into Photoshop, but if that’s not possible, here’s a Photoshop trick that will help you identify a neutral point then fix it. Create a new layer [1], then go to ‘Edit > Fill’; choose ‘Contents: 50% Grey’ to make a grey layer [2]. Change the Blend Mode [3] of the Layer to ‘Difference’.

Now you need to identify the darkest areas. Click the Adjustment Layer icon [4] and choose Threshold [5], and drag the slider to the left [6] so that only a few tiny black points are visible. Grab the Color Sampler tool [7] and click over the black area, then hide both the top layers. Add a Curves Adjustment Layer [8], then grab the Curves grey point eyedropper [9] and click on the Color Sampler point [10] to correct the colours.