Thanks for the feedback and we understand the issue that you raise. The reason we went with the flat WebEx icon is that we are trying to avoid mixing metaphors in our control areas (pictographic iconography vs. photorealistic iconography). When we mocked up our UI using the multi-colored WebEx ball it overwhelmed the rest of the controls and caused some usability problems.
We are currently in the process of reconfiguring the share/WebEx UI at the top of the screen to address this problem by consolidating all of the share options into a drop down menu with text labels that will make the available options much clearer and avoid any confusion in terms of icon meaning.
Look for this updated UI in a post 9.1 release.
Mark