With MCAD as prevalent as it is now, I think you'll see an acceptence of this practice. I don't know of any standard that "forbids" its use. Drawings are suppose to be unambiguous, if shaded views get you to that point, all the better.
Back in the drafting board days, I can remember doing ink-washes over some details or parts in exploded views in order to either make them stand out or to suppress their visibility to make other things clearer.
Recently, I have used color shaded views in a plan view of an assembly to make parts stand out from others, instead of just looking like a bunch of parallel lines.
[green]"I think there is a world market for maybe five computers."[/green]
Thomas Watson, chairman of IBM, 1943.
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