[GRASS-user] raster drape color question

[Ken]

I'm a total grass newbie.  When I drape a map over my base dem map the 
"draped" map blows away my colors in the dem map.  Even where the drape 
map doesn't appear to have any values. (the dem map seems to get a sort 
of grey tone in those areas)  Is there a way to preserve the color map 
from my base map and have the drape map only overlay the colors where it 
actually has values?  ie: is there a transparency color i can set?  the 
"(transparent null value cells)" checkbox doesn't seem to change anything.

thanks!
ken