This happens because KDE's defaults apply its color and font
definitions even to applications that weren't compiled for KDE. The
solution is to uncheck the "Apply fonts and colors to non-KDE apps"
-option in Preferences->Look&Feel->Style.
+option in Preferences->Look&Feel->Style (KDE 2). In KDE 3, this option
+is in the "Colors" section, rather than "Style".
Alternatively, if you do want the KDE defaults to apply to other
applications, but not to Emacs, you could modify the file `Emacs.ad'