The result you describe is by design - the background of the timeline is applied to the area of the control beneath the line, separating the two rows of intervals. Basically, in case you are using the Expression_Dark theme, I suppose the background of your whole page is dark and thus the text should be visible. There are several approaches, in case you want to use a specific background for the top most header of the controls, the simplest of which is to wrap the control in a Border and apply the background to that border. Have a look at our Theming demo for a reference.
the Telerik team
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