Nested polygons in QGIS overlap and don't show the real colour gradient

I am working with nested polygons in QGIS and each of them has got a specific let's say n (numeric) value represented with a given colour gradient.

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  All my polygons are loaded into one shapefile

  
  


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  If I use Feature blending mode = Normal I miss (don't know why) some of the nested polygons, but colours are ok, see below:

  
  

  

  
  


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  If I use Feature blending mode = Multiply QGIS shows me ALL the polygons BUT for all of them their colours overlap and their areas become darker than the reality, see below:

  
  

  

  
  
  

What I need is to show ALL my polygons with their real (not-overlapped) colour gradient.

Is there a way I can get around this?

Answer

To modify the above topology, you need to use GRASS -> v.clean from Processing toolbox -> GRASS GIS 7 commands -> Vector -> v.clean, and in cleaning tool use Break, as you can see below:

You may need to re-enter the values in attribute table after cleaning your polygon shapefile.

You can refer to my answer to the question: Cutting all polygons with each other - mega slicing for illustrations.