Reread what I wrote...
It works on ALL materials, making the RGB values 235 maximum; thus 'toning down' the hue of every color that has an RGB value > 235.
To use this one-liner code... open the 'Ruby Console' in SketchUp [via the SketchUp > Windows menu] and the copy/paste the whole of the line of the code into the bottom area of the 'Ruby Console', then press the <enter> key to run it.
All materials are changed [it's relatively fast].
You should see the RGB change in any material you 'Edit' in the Materials Browser, if any value was > 235 it will now be 235...
It is one-step-undo-able - e.g. if you decide you don't like the changes.
You could save the one-line of text into a text file for easier use later on...