Yes it's a know fact the sun bleaches everything on earth but case colors on guns.
Does the sun bleach snow? Or water???... how about water? Is water deep in a cave lighter in color than water under a tropical sun?
Oh, of course... snow and water have no pigment. So let's consider some things that do have pigment, like rocks. I notice that most rocks don't get bleached by the sun, or are typically darker on the inside if you break them. After millions of years of exposure to sunlight, shouldn't all rocks on the surface be bleached white by now? Same goes for sand, which will be the same color a foot deep as sand on the surface exposed to the sun.
How about grass? Does grass turn a lighter green or get bleached out when exposed to the sun, or when it is deprived of sunlight?
And does the sun bleach skin, or does it make skin turn brown? Shouldn't Nordic people be much darker than indigenous Equitorial African people? Ever seen a black person with a tan line after exposure to the sun? I have.
The sun will cause anything to fade eventually
Even on the moon, there are both light and dark colored rocks and dust, whether on the always illuminated near side, or on the perpetually shaded dark side. Clearly, there is more involved in color retention than simply exposure to sunlight.
But to kinda get back on topic, it seems the jury is still out on sunlight damaging case colors, and nobody has done any definitive testing to prove what is often stated as fact. It appears that there are a lot of other things that cause them to wear, fade, or become obscured. I'm still blown away by some of the results we've seen here that restore a lot of case colors by simply cleaning in an ultrasonic tank. That process probably deserves more study too. A couple days ago, I watched a YouTube video where a guy tested 8 different ultrasonic cleaning solutions by individually cleaning the filthy carbon crusted pistons and rods from an old V-8 engine. There was a wide range of results from the same ultrasonic tank, ran for identical times. Surprisingly, one of the very best performers was Cascade dishwasher pods, and the cost per gallon of solution was much cheaper than several of the more highly touted specialty brands. So the same could hold true for ultrasonic cleaning of case colored gun parts too.
