I've tried to do some search in forums and over the internet but I haven't found anything visual enough to understand what exactly unpremultiplication does and what's more important - what is it's use in Terragen in default shader for example? I'm inspired to ask this question as I've stumbled upon those over bright textures on some models with unpremultiply colour enabled.
This discussion (and the pages linked to) cover it pretty well: http://www.xsibase.com/forum/index.php?board=12;action=display;threadid=24137
- Oshyan