Bhop, that is true. But it takes a while.
Paint is a science. It has a base, a catalyst and a reducer (thinner).
US OD 24087 Semi gloss olive drab used by armor from late 43 on and by all US Army equipment through Vietnam, has a couple different mixtures from manufactures. One type will fade to pea green the other will fade to brown and then finally pink as the sun burns the pigments out of the base., while the last one actually fades to black.

This kind of fading takes a few years to many years. I have two US Army vehicles out front of my house that I have watched fade. Its an interesting process. I have also worked on many many vehicles and seen and photographed a huge number through their paint life.

It takes a few years for the first fading to start, especially with paint that still has lead in it. Lead was a binder in the base, it is gone now from paints but back when it was used paint lasted so much longer before it faded. Also, older lead paints could be revived with a good scrub washing.

During WWII, fading would not be that significant in ETO from 43 to the end of the war.
Paints should be pretty darn close to what the original color was before gime and dirt are added if you want to be accurate.
MTO in North Afrika might have experienced a little fading due to lots of sun and reflected desert heat.

But, its your tank, do what makes you happy. Hence why I spent months trying to mix various testors OD colors to get the right OD because I know their 24087 is not right. I finally switched to Tamiya and kept going, and then decided to start with the basics. Olive drab is two colors. black and ocre. Ocre isn't available to I add yellow to brown to get ocre, throw in black and I get a super awesome dark OD that looks brown in the dirt and green in the grass. Over coat with some gloss if its late 43 or later for when they switched from flat to semi gloss and its sheen gets darker but its still the same color. Beautiful to my eyes as to what the OD is supposed to look like. Many WWII US soldiers said their tanks were more brownish color than green. They were not the same color as wheeled vehicles, which is pretty close to the testors 24087.

Any way, I know your not trying to mix OD but this is my saga of paint.