The star is darker because there is a light haze or fog over it. It's dense enough to scatter the light from the sun, but thin enough that it's not visible to the naked eye. As you move up the tower you move out of the mist, thus the sun becomes brighter, just like the sun becomes brighter if you're ever taken off in an airplane and it becomes brighter as you gain altitude.

Simple as that. No fancy meanings or hidden symbols. Just basic physics at work. Sorry your theory turned out to be a realistic representation of mundane life.