[AUCTeX] Fontifying macro arguments...

[Robert Goldman]

I would like to be able to change the face used to display the ARGUMENT to a
latex macro.

In particular, we commonly use \hide{} to wrap old text that we are not
formatting.  This is less cumbersome than the % line comments, but it's hard to
tell if large blocks of text are active or not.  So I would like to gray it out
by assigning it a face like "shadow."

I thought that font-latex-user-keyword-classes would let me do this, but it
seems like it sets the face for the keyword itself, rather than the arguments.

Is there some way to set argument fontification?

Thanks!