The function set-application-themed controls whether a LispWorks application should be themed.
On supported versions of Microsoft Windows, LispWorks is "themed", that is it uses the current theme of the desktop. You can switch this off by calling
(win32:set-application-themed nil)
On systems older than Windows XP (no longer supported), or when the application does not have Common Controls 6, this call has no effect.
set-application-themed affects only windows that are created after it was called. Normally, it should be called before any window is created, so all LispWorks windows will appear with the same theme. However, set-application-themed can be called multiple times in the same run.
LispWorks User Guide and Reference Manual - 20 Sep 2017