Projector

[neon22]

The reason this works is that cloud density is similar to opacity. The opacity can be different in each colour channel.

The way Terragen's density shader works is that it also affects the shape of the cloud. But if you want to control the density in a straightforward way without changing the shape, you can use the final density modulator plug instead of the density shader plug.

I first saw this (colour in density shaders) in a tgd called "From Orbit.tgd" here:
http://forums.planetside.co.uk/index.php?topic=3691.msg110938#msg110938