Hi,
I am using Radgrid with office black style and am applying a sort descriptor from code, this results in the column header of the sorted column being a different colour from the rest how do I change the default behaviour so that the header is the same as the others?
You should try to predefine the template of GridViewHeaderCell using Expression Blend and change the GridViewHeaderCell_Selected which represent the header when it is selected. For more information check this help article which shows how to style RadGridView Header Cells. For your convenience please find attached a sample demo which meets your requirements.