Hello Jörg ,
Thanks for contacting us. The reason for this behavior is that a theme for RadLabelElement is not defined. I have attached the required theme. You can easily use it by loading it from RadThemeManager component. Thus, each time the Office2007Black theme is applied to a RadLabel control which is in a RadStatusStrip control, this Style Builder Info will be used (which actually defines the white Fore Color for the RadLabel control).
We are also going to update the Office2007Black theme for the RadLabel control to support this behavior.
I hope this is helpful. Do not hesitate to write back if you need further assistance.
the Telerik team