I am answering my own question here I think! Using a RadCalendar to create options to set a delivery date...
I have successfully got Todays date formatting working - however I needed todays date to be below the RangeMinDate (ie the earliest one can choose is tomorrow).
However - As soon as you do that the css disappears for todays date!
As a solution You can allow today into the range
RadCalendar1.RangeMinDate = DateTime.Now()
and then set
<telerik:RadCalendarDay Repeatable="Today" Date="" IsSelectable="false" ItemStyle-CssClass="rcToday">
Seems to work for me! Apologies if too obvious!