I'm currently testing this on my slightly odd colored Ravello PTB's. It's been almost a week of the darker one sitting out on a window sill, but unfortunately it's been cloudy almost that entire time. I'm going to leave it there for another 2 weeks at least - I'll be sure to post the results here.
Thanks hoit. Mine are also ravello and would not have been available NIB at my price point without the color variance. Fortunately it's only noticeable to shoe junkies and in certain light. Having said that, I'm willing to give this a try if it makes sense.
I'll be looking for your results. Again, thanks for the response and good luck.