Richard, thank you for your assistance.
Jim, at the time when the Aqua theme was created, there was no support for a threestate checkmark. Recently, we introduced a new theming mechanism and we switched most of the predefined themes to it. Aqua, Telerik, Vista and Breeze themes, however, are not updated according to the new styling rules.
We plan to update Aqua and Telerik themes in one of our next versions. As to the Vista and Breeze themes, please consider them as obsolete and use Windows7 and BreezeExtended accordingly.
In regards to your specific question about the Aqua theme, as I mentioned above, it is not supported by the the theming mechanism. However, you can modify the FillPrimitive of the checkbox which will allow you to distinguish the On
state from the Intermediate
one. For better understanding, I am attaching a sample project where the modification is applied. If you decide that this theme is suitable for your application, you should load it in your project as described here
I hope this helps.
the Telerik team