75% will work for Domincans and non Cuban smokes, but I bet after about 73% with Cuban cigars you'll be looking at mold. 62% (some mistakingly believe is too dry) - about 70% rh is what I maintain prefering cigars that have been at an extended period of under about 66%

A change in ash color was noted. I'd be curious to know if you felt the ash burned a little darker and less white at the higher rh level. My assumption is because of the higher moisture, the tobacco would be less combustible and burn less complete leaving a darker ash behind.

Lastly as some suggested, you're hydrometer might be slightly off. If you've been used to cigars being stored 70% or below, I´m sure 75% would at least yield a few noticable differences.