Both the Window QML type, as well as the Rectangle type have a property color. However, a Window expects premultiplied alpha, whereas Rectangle expects straight alpha. This is inconsistent, confusing and not documented.

In the attached QML code, the inner window color is "#80008000" and the rectangle color is "#8000FF00" (different green channel). Still they appear the same.

Ideally this could be harmonized or at least documented.