The article for AppointmentStyleSelector is a little bit outdated - the approach works but as you've noticed, you should copy all the referenced resources in the xaml file in order to customize the appointments' style.
However, in the latest versions of the controls (since Q1 2012 SP1), there is an easier way to make such changes with the help of Implicit Styles - detailed information on the approach can be found here
. This approach is used in our online demos, actually. Using implicit styles you will be able to create custom Styles based on the default ones and change only certain properties. I have prepared and attached to this thread a sample project showing how you could change the color of the appointments based on a resource. Please download it and give it a try. Note that you should reference .NoXaml assemblies.
Hope this helps.
the Telerik team