I've created a roll-up worksheet within a workbook.

Numerical results are posted to C1 using results from B1/A1.

If numerical data in C1 is < 65% cell color in D1 turns red
If numerical data in C1 is 80% cell color in D1 turns green
If numerical data in C1 is 66% but < 79% cell color in D1 turns amber
Used conditional formatting and the following formula to create above results.
=LOOKUP(B1/A1,{0,"R";0.65,"A";0.8,"G"})

Would like to capture a fourth category in cell C1 (if possible)

If the numerical data in C1 has 0 (zero) value. Is their a way to configer
the cell color in D1 to turn white?

Would like to create a formula that will show the 4 colors in D1 based on
the above assumptions.

Thanks