How to make a positive summation show red

Hi,
I want to be monitoring stock position through daily sales. If the stock level gets to a certain level, i want the daily sales summation to turn into red if it gets to a red alert level even if the summation is still a positive number.
e.g
s/n product name Re-order level opening balance. closing balance. monday. tuesday. wednesday. thursday. friday total
1 candy 3000 3500 3000 350 25 25 50 50 500
in this case i want my closing balance to turn into red colour.
thank. kind regards