I've used Jim's suggestion a couple of times since he told me about it a few years back. But the last time I wanted to dampen the colors, I wanted to take more off the high spots and the wide flats of a "thin side" highwall, but leave a bit more of it in the corners and concave surfaces, so I put a bit of semichrome on a glove and just fondled the action for a while (an "a while" is only a few minutes). The net result is more of an appearance of normal wear and less like the uniform French Grey that some folks prefer.
Anyway, it worked for me.