This is a simple "whitepoint" correction plugin. It's ideal for images which have a slight color tint, and which contains some pixels which should be neutral grey.
I wrote this plugin as my mobile camera usually ends up taking images with poor color balance, and I wanted a simple tool to correct it. I'm publishing it in case anyone else finds it useful.
Select the Color Picker tool.
Use the Color Picker to select a Primary Color which should be neutral grey.
Select the Adjustments menu and select the Whitepoint plugin.
If not satisfied, undo, try another color and run it again.
Here's an illustration image.
How it works:
The plugin will apply a photo filter-like effect on the image using opposite color of the selected Primary Color, while preserving the brightness of the source color. For example, if the Primary Color is blue-green (cyan) it will apply a red photo filter.
Distributed under the LGPL license, the .cs file is for use with the CodeLab plugin, ignore it if you don't want to look at or modify the code.
Note that picking a color from a uniform area works best, the brightness of the color is much less important. For the example picture below I picked a color from the shadowed area on the napkin, as can be seen in the illustration image above.
For images with a lot of color noise it may be beneficial to downsize the image before picking a color to get a better basis color for the filtering. Undo the resize after you've picked the color.
As always "garbage in = garbage out". This filter cannot undo destructive processes, so for example washed out highlights may not look good. It works best for images with a slight tint.
Hope you enjoy