add abr color dynamics

src/app_layout.cpp

@@ -150,7 +150,9 @@ void App::init_sidebar()
         stroke->set_size(value, true, true);
     };
     quick->on_brush_change = [this](Node*, std::shared_ptr<Brush> b) {
+        auto c = Canvas::I->m_current_brush->m_tip_color;
         *Canvas::I->m_current_brush = *b;
+        Canvas::I->m_current_brush->m_tip_color = c;
         brush_update();
     };