Setting the background color for image services to 'No Color' results in a gray background

Description

If you change the background color of an image service to 'No color' on the symbology tab of the ArcMap Layer Properties dialog box, the background will appear gray.

Cause

ArcIMS and ArcGIS define 'No Color' differently.

Solution or Workaround

1. Open the image service layer Properties dialog box.
2. Click the Advanced tab.
3. Check the 'Background transparent' box.