Today’s Question: What is the best way to remove yellow from photos when the photographer did not use a flash?
Tim’s Quick Answer: There are two approaches that will likely help here. You can apply a strong shift with a Temperature adjustment, or use a technique for removing a strong color cast in Photoshop.
More Detail: The first approach would be the simpler. Very often in this type of situation simply shifting the Temperature slider significantly toward blue (away from yellow) will provide a good solution. This is possible even if the photo was not a RAW capture. For example, you could use the Camera Raw Filter in Photoshop, even with a JPEG capture. The same adjustment is also available in Lightroom and other software tools.
If the color cast is too strong for a simple Temperature adjustment, then I’d employ a helpful technique in Photoshop. Start by dragging the thumbnail for the Background image layer to the “Create a New Layer” button (the blank sheet of paper icon) at the bottom of the Layers panel.
Next, choose Filter > Blur > Average from the menu. This will process the Background Copy layer so that it contains only pixels of a single color, representing the average color for the full image. That is essentially the color of your strong color cast. You need the opposite color though, so choose Image > Adjustments > Invert from the menu to invert the color to the opposite value.
Next, on the Layers panel, click the popup at the top-left of the panel (the default value is “Normal”) and choose “Color” from that popup. This will set the blend mode for the Background Copy layer to Color, which will cause it to alter only the color (but not the tone and texture) of the underlying image.
Finally, to reduce the strength of the new color cast, reduce the Opacity setting for the Background Copy layer using the control at the top-right of the Layers panel. Start at a value of about 50%, and fine-tune from there for the best color.
With either of the above adjustments you may need to enhance overall saturation and contrast to compensate for other issues in the image. But the strong color cast should be something that can be resolved with one of the above approaches.