Picture fill in pivot charts

Hi, I am changing the fill in a clustered column chart to show a background of a country flag. I have done this for four countries but when I select a different country it always brings in the fill as the last background I used. This is annoying as in total I have around 120 countries in my data set and I don't want them all to show the last background I set.

This also happens for an ordinary fill and doesn't seem to stay fixed to what I have chosen.

I hope this makes sense and that there is a n easy way of stopping this from happening.

Thanks for your help.