[thredds] WMS off scale color

Hello, I was wondering if there was a way to customize the color used in a WMS 
image when the data is outside COLORSCALERANGE? It seems the default is black. 
This does not seem to be the same as the background color, which is transparent 
(using transparent=true). In the end I get transparent where there is no data 
and black when the data is off the scale. Is there a way to make them both 
transparent?

Thanks

-- 
Jay Alder