David,

You can set the Transparency, or set a different color to the layer, or both.  It's entirely a matter of preference, and many of those who created office standards, did so before Transparency was even an option.  The nice thing about using Transparency rather than a color change, is that you can uncheck Plot Transparency to return everything to its previous state.  Meanwhile if you change the layer's color as an override, you would need to save Layer States to toggle back and forth.

--J

Great! I appreciate the speedy response.

Normally I enter the paperspace viewport, use the layer filter in layer manager to select the layers in the xref I want to alter, then change the VP Color for those layers to a color in my .ctb file that has the level of screening I prefer. 

I didn't realize that this could also be done with the Transparency setting.  Will have to give that a try.

At least once, and I don't remember exactly how or why, I used a partially transparent wipeout to control the visibility of the layers behind it.

But this is a good question, and I'd also love to hear if anybody has another preferred method.