Changing font color


I need help, I want to change the font color to be black for cell A, if cell B is "done", else keep the due date in red in cell B.

For exmp:
Cell A1 =today()
Cell A4 due date is 4 March 2017 (red)
Cell B4 is keep counting the over due days
Cell C4 is where the payment is still in debt. But once the payment is fully paid, then cell B is "done" automatically. When cell B is "done", the due date in cell A is black again instead of red.

up to now i am using the format for cell B with =IF(C4<=0,"selesai ",(A4-A$1)
For Cell A4 I am using Conditional formatting rules manager

I am using windows 10

Thank you