Column option grayed out, impossible to apply my vector designs within a graph

I created and I need to applying a graph column (in these case the orange rectangle but the option is always grayed out so basically I can't go ahead.

How can I fix it ? The orange rectangle is just a simple example, obviously I can change the fill to the other rectangles in this case to solve it, problem is I need to apply it to vector illustrations. And I didn't understand why is always grayed out because from there I can apply whatever vector illustration I need.

Thank you in advance.