[R] "Over-coloring" facets on persp() plot

[Marc Chiarini (Tufts)]

Dear R Community:

Recently, I have managed to plot some really useful graphs of my 
research data using persp().  I have even figured out how to overplot 
rectangular regions (corresponding to submatrices) with a different 
color.  This is accomplished by using par(new=T).  I am now searching 
for a way to "highlight" a set of (possibly non-contiguous) facets with 
a specific color, e.g., the facet between each set of four points whose 
values are all above a certain threshold.  An example would be coloring 
the raised corners of the classic sombrero (found in example(persp)) 
differently from the rest of the sombrero.  I feel like the last example 
in persp() is pointing me in the right direction, but I'm not quite 
getting it.  Any help is much appreciated.

Regards,
Marc