Due to a bug in the 9.2 .NET Web ADF, in-memory GraphicsResources that use the default image format of PNG8 do not actually use the PNG8 format. The image format returned consists of PNG32 images using 24-bit RGB color and 8 additional bits for transparency.
This bug has been addressed for 9.3.
Due to this fix, the PNG32 format should now be used on graphics resources when using semi-transparent symbols on graphics layers. The default format of PNG8 only supports 1-bit transparency, meaning the image is fully transparent or fully opaque. PNG32 is the only image format that supports semi-transparency.
See the example below:
Semi-transparent fill symbol using PNG8 (left) and PNG32 (right)
This is not to be confused with the transparency setting on the DisplaySettings of the MapResourceItem. This property did not change and allows a single transparency value to be applied to a whole resource regardless of the image format.