If upp can listen to the event and request all Ctrl to Refresh (hierachically) themselves, and all SColorXXX returns a reference (to a static variable who has application-long life time which will by updated by Upp at theme-changes), a upp application can behave more similar to a native gnome/x11 application.

However, all user programs alos need to change accordingly to use Color& instead of Color to store SColorXXXs that they use in their own chameleon style. But this won't break their programs catastrophically even if they don't: any part that they call SColorXXX on the site will be reflectly after first Refresh, while the part they stored a copy of SColorXXX, in, for example, a Chameleon style, will only be corrected after a restart.