2-D 3-layer bar graph

Here is another approach to the problem using custom fills.

All columns are on the same axis. With overlapp set to 100.

I created to grouped shapes to use as the fill.
The group is a rectangle with no border or fill. Make this roughly the width of a column in the chart.
The second shape is a thinner rectangle coloured as appropriate.

With the 2 shapes grouped you can use copy and paste to fill the column series.