Textbox is the only way I know of, but you are telling us you do not want that because of exporting to Xls.
Could you tell us why you want to export it to xls? Sometimes the answer is something that can be done in QlikView instead.
Alternatively, you could look into making an NPrinting report and doing it that way.
No, I had a same experience in my project and my solution is make all the columns heading to this grey colors.
for doing that first of all
1. Click the Design grid option in the design tool bar which is next to paint brush.
2. right the chart and you will get the "custom format cell" ensure your self that "design grid is selected".
3. In the window select "background" and adjust the color to the grey color.