where is the problem?
Qt Code: 
  1. QPalette* palette = new QPalette();
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In the first case, this is a memory leak. You should simply retrieve the existing palette from the widget:

Qt Code: 
  1. QPalette palette = final_angle->palette();
  2. palette.setColor( /* whatever */ );
  3. final_angle->setPalette( palette );
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And if you read the QPalette documentation, you will see that QPalette::Background is an obsolete ColorRole. You should probably be using QPalette::Window or QPalette::Button; I don't know how painting in QLCDNumber is implemented, so I don't know which role it uses to paint its background.

You do read the documentation sometimes, don't you? Or do you just simply post a question for every problem you run into?