ok, i figured it out
i have to do this for each cell seperately but i select each cell, then go to home, and select "conditonal formatting"
enter a new rule, only cells with a certain value and then i say value eqaul to
at this point i drop in the formula (for E20, it was (D20-A21-A22-A23-A24-A25-A26-A27-A28-A29-A30-A31) )
and i replace the cell name with a 0 (so now it becomes =(0-A21-A22-A23-A24-A25-A26-A27-A28-A29-A30-A31)
then under format i hit font color white, and boom, bob's yer uncle
while i was at it, i also dropped in a conditional format that all numbers below 0 are red, and above are green