I've tested the behavior I have sent you only with the default theme of RadCalendar. After your response, I've tried it with the other themes too. If there is a special coloring for the other months' days, you can use the following:
void radCalendar1_ElementRender(object sender, Telerik.WinControls.UI.RenderElementEventArgs e)
if (e.Element as CalendarCellElement != null)
(e.Element as CalendarCellElement).Today = false;
(e.Element as CalendarCellElement).OtherMonth = false;
As you can see, the CalendarCellElement class has a special behavior in different situations depending on selection, today's date, other month date, etc.
I hope this helps.
the Telerik team