I'm not sure how the presets you're talking about are set up- but if you click on the right-most button in the sky and fog pallette enough times (or drag on the arrow, same difference), you will get a setting with a single color bar across the bottom (or 'atmosphere off). You can then set the sky color from there- and you can set more accurately by option (alt.) clicking the color field. This should produce a uniform background without haze effects, etc. Hope this helps! Gecko