It has been happening to me also.
I started about June, holding up a bottle of honey to the sky exactly at 6 o'clock pm. And each and every month, it got darker and darker. I made sure the bottle was held up at the same time every month at exactly 6 pm. And I kid you not, each month the bottle got darker and darker. By October, that honey was almost pitch black. I threw it out. Still has me scratching my head. :roll: