Utils: Improved handling of StyleHelper::baseColor

This change makes sure that the "UI coloring" feature respects the
original brightness of the current theme. It prevents dark themes from
getting a too light recoloring and vice versa.

Extra benefit: this allows to remove much recently introduced code.

Change-Id: Ib2c96e7ed172a4cc97520aa4b5d180cc6353c661
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/coreplugin/progressmanager/futureprogress.cpp

@@ -296,9 +296,7 @@ void FutureProgress::paintEvent(QPaintEvent *)
 {
     QPainter p(this);
     if (creatorTheme()->widgetStyle() == Theme::StyleFlat) {
-        p.fillRect(rect(), StyleHelper::isBaseColorDefault()
-                   ? creatorTheme()->color(Theme::FutureProgressBackgroundColor)
-                   : StyleHelper::baseColor());
+        p.fillRect(rect(), StyleHelper::baseColor());
     } else {
       QLinearGradient grad = StyleHelper::statusBarGradient(rect());
         p.fillRect(rect(), grad);