In XFramePeer.java and MFramePeer.java the methods
public void print(Graphics g);
have comments :

    /*
     * Print the native component by rendering the Motif look ourselves.
     * We also explicitly print the MenuBar since a MenuBar isn't a subclass
     * of Component (and thus it has no "print" method which gets called by
     * default).
     */

...
// Well, we could query for the currently running window manager
// and base the look on that, or we could just always do dtwm.
// [various names] all agree we'll just do dtwm.

This may have made sense for the Motif toolkit in 1996 but it makes no sense these
days where users on Solaris are most likely to be running the Gnome desktop
and on Linux could be running that or KDE or similar.
We should at the very least have the peers support Gnome if it detects Gnome.
Conceivably we'd need to track how the frame is rendered by the theming engine
If we support KDE in dolphin that should be supported too.