Automatic alarm with red colour

I have two excel sheet. In sheet1 (index) and in sheet2 customer data.

I want in sheet1 column f2 automatic change colour with written "due for alarm".
If today is : 20-dec-09
in sheet2 next due date is 21-dec-09
when i open file on 21-dec-09 automatic showing in f2 with message "due for alarm"

i have attach file for your ready ref.