do real AFVs actually take on the same kind of colour shifting?
In a word, no...
That's pure artisic license, since most guys that do that seem to be trying to recreate the lighting in a particular photograph and to also add their own artistic "look"... I don't see it that way... Nor do I find mono-chromatic finishes "boring", other than for the reason that they are supposed to be "boring"... Combat vehicles are not supposed to attract attention to their lines and shapes, and crews go to great lengths in order to hide those shapes and lines...
Just go look at your parked car under various lighting conditions and times of day... YOU know what color it actually is, yet as the light changes, so do the "shades" of color... Yet nothing has actualy changed on the vehicle...
Frankly, the only way that it looks good to my eye is in a shadow-box diorama, where the lighting is controlled and the viewpoint restricted... Otherwise, it looks like what it is... Dfferent shades of color applied here and there... That's fine if your going to paint something that has three dimensions, but your primary method of displaying it to others is to show it in two dimensions, i.e., a photo... Otherwise, let the ambient light do its job, I say.... Lotta times it looks even worse, since the room light it was painted in isn't what it's displayed in... But it does look great in photos though, I admit...
While figures often need shadows and highlights added, a scale tank or other AFV doesn't need that kind of shading... The result of painting shadows on vevicles is rather "Comic book-like" art in my humble opinion... But if you enjoy doing, that's ok... Just be aware of the fact that ya ain't fooling me, lol..