FIX: Support dark mode in filament picker

- Applied dark theme styling to filament picker dialog
- Fixed color picker background not updating on theme switch

jira: STUDIO-12935

Change-Id: I9c7dcc518e7b0bd2c330f477ee42f4c61ea9fd4b
(cherry picked from commit 66ae7a02b945ff603b2dc699c93e55589481379e)

src/slic3r/GUI/PresetComboBoxes.hpp

@@ -209,6 +209,7 @@ public:
     FilamentColor get_cur_color_info();
     void show_default_color_picker();
     void sync_colour_config(const std::vector<std::string> &clrs, bool is_gradient);
+    void sys_color_changed() override;
 
 private:
     // BBS