How to turn off Outlook sort shading?

[wmlady]

My computer & my co-worker's are both running Outlook 2003 / WinXP. On my computer the Received message sorted column is shaded slightly gray while on my co-workers there is no shading. Both computers show the triangle indicating ascending or descending sort. On the one with shading, the sorted columns are consistently shaded in all folders even if sorted on multiple columns. Does anyone know how to turn the shading on or off?

Thanks in advance,
Wendy