title: ag-grid : How to set custom background color in column header?
body: <p>I'm using ag-grid with Angular 4.
  I want to be able to change the background color of individual column headers during runtime. </p>
  
  <p>It seems that I have to use headerComponentFramework property in coldefs, but I have no idea how to use this.
  Anybody has an idea?</p>
  
  <p>regards,
  Alex</p>