Here's how it's going so far:
This is an up-close. The ebony I used in place of caulk is loose on the left side. I'm not sure if it's the ebony or the teak/mahogany that's changed, or both.
FWIW, I used applied Defy to our hot tub steps a few months before the test
wood. The steps were subjected to the chemicals that comes off wet bodies exiting the hot tub.
These steps, when unfinished, would turn dark brown in a few months and silver after that.