This isnt a theme or a hack.. Its (to my knowledge) an undocumented feature of KDE.
You can change the colorscheme, theme, fonts and many other elements of individual KDE apps on your desktop as my screenshot shows.
Its done by adding some lines to the program in question ~/.kde/share/config/*rc file.
For instance konqueror, which uses ~/.kde/share/config/konquerorrc
if you were to add the following lines:
You would have a konqueror that would use the above colors and theme regardless of the rest of your desktop.
You can also change, fonts, icon theme, mouse preferences.. almost anything.
If you want to know all the available options look in ~/.kde/share/config/kdeglobals
Dont like all those numeric color values? u can always make a color scheme kcontrol/colors and then use
I dont know if this is well known but I certainly havent ever seen someone use this, so experiement and have fun.