The background color of a Web site will be obscured by any Image MapService that has a default (opaque) background. Similarly, if you want to use more than one Image MapService in a Java-viewer Web site, the opaque background of the initial Image MapService will obscure the other Image MapServices.In such cases, you must set the background to a "transparent color" in the Map Configuration file for each Image MapService. As well, Image MapServices must use either the PNG or GIF image format.
<BACKGROUND color="255,255,255" transcolor="255,255,255" />
<ENVELOPE minx="-122.5134" miny="37.7082" maxx="-122.355376" maxy="37.8325" name="Initial_Extent" />
<MAPUNITS units="decimal_degrees" />
}<BACKGROUND color="255,255,255" transcolor="255,255,255" /
It is not necessary to use "255". Any valid value (0-255) is OK as long as the RGB value for the color attribute is identical to that of the transcolor attribute.
Get help from ArcGIS experts
Download the Esri Support App