ASP.Calendar cell back color based on the amount of appointments on specific date

Hi all,
This question is pretty basic, all I want is some guidance on setting the cell backcolor based on the amount of appointments on a specific date.
IE.
On 12-06-2013 I have 5 appointments
And on 13-06-2013 i have 2 appointments
What i would like to do here is setting the cell in 12-06-2013 to yellow and the cell back color of 13-06-2013 to green.
Consider the colors as an indicator trying to explain if a certain day is free to receive appointments or is almost full of appointments.
I got my database set up already
Thanks in advance!
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