persp and lines()

R-sters:

I'm interested in keeping data plotted in persp to preserve the wireframe 
look, I'd just like to change one of the lines drawn (in either the x or y 
direction) into a different color so that it stands out.

Or is there some way to add a line (say, via lines(), or abline()) to a 
persp() plot at the designated x or y that would follow the z surface 
contour?  I could add a line using 2D representations of the data, but I'd 
like to use the perspective plot if possible.

Any advice?

Cheers,

Jeff