Another reference for datetime picker in gridview review this link;
Windows DataGridColumns User Controls[
title="New Window">^]
for the second question this is a good link to start with;
changing the background color of the calendar control[
^]
you should take a look at Calendar.SelectedDates and Calendar.SelectedDayStyle properties
colorMyCalendar.SelectedDates.Add({DateTime object});
colorMyCalendar.SelectedDayStyle.BackColor = System.Drawing.Color.Yellow;
If you want to color specific dates in the month, then you should take a look at
Calendar.DayRender Event.