When a conical warp is applied to a image in Adobe® Illustrator® using the Studio Toolkit for Labels, there are considerable differences in the colors.
Solution
This happens if the 'Anti-Alias' setting is enabled in the Envelope Options dialog. Disabling this option will resolve the color issue so that there are no more color differences compared with the original un-warped graphics.
The Anti-Alias option can be found in Object > Envelope distort > Envelope Options.