You can also use "Appearances" which is the easiest way IMHO.

Cheers
Aaron

            Dim AP As Infragistics.Win.Appearance
            ' Create an Appearance for each day you want to look "different"
            AP = Me.CalendarInfo2.Appearances.Add("SpecialRedDay")
            AP.BackColor = Color.FromName("Red")

            Me.UltraCalendarLook1.DaysOfYearLook(Now().Date.Appearance = _
            Me.UltraCalendarLook1.Appearances("SpecialRedDay")

Investigate: Infragistics.Win.UltraWinSchedule.DayLook

 There is a fantastic example supplied on how to change Appearances of timeslots/days/weeks/appointments/months/alternate days etc 

 C:\Documents and Settings\All Users\...\Samples\WinForms\WinSchedule\VB\Appearances

 If you really want to get tricky look at the following KB Article:

Knowledge Base Article: KB05595
HOWTO:How to use a drawfilter to customize the display of the UltraWinSchedule day and timeslot elements.

<Link to Article Here>

 Hope this helps

You can infact do it in your code by comparing current date.