How to format data in Excel export?

I want to export data to Excel. Is there any way how to format cells in ExcelService WriteSheet method?
For example I want to set cells background color based on cell value or entity field value. Or just make the text in the cell bold.

It is not directly possible with the current functionality. What you can do is to export data to a special sheet and use preformatted Excel template and retrieve data from the exported sheet using formulas.