Thanks for the Oxalic Acid lead. I tried it on two timbers and it has indeed lighted the mold stains somewhat -- without bleaching the timber too much. I noticed the directions on the bottle mentioned the "full treatment" bleaching. Since the stains were not totally removed, and I'm a curious fella -- I'm going to try the "full treatment" to see what that looks like. Stay tuned.
I'll still take leads on any interesting colored/stained finishes that anyone knows of.