Aha aha aha.

Now look at Rochr's screen shot and you can see why adding ambience makes things look pale. Ambient colour is set to white! Put another marble in column A against Ambient, so that it takes the texture for both diffuse and ambient illumination, and set the ambience to about 12.

Looks better now!

Using weak texture ambience this way makes objects look more vivid, and gets rid of very heavy shadows where no light is falling. It's a poor man's radiosity, in a way.

The only time I ever set ambience really to zero is in a dark interior where I want, say, walls to recede into utter darkness with distance.

Incidentally, if you have a look at the default Bryce materials, some of them have really stupid ambience settings. "Light wood" is about 40 if I remember correctly, which means that any objects with this unmodified material pop out in darkly lit scenes. These materials have shipped unchanged ever since Bryce 2 and no-one has ever fixed them!