Try something like
if workbooks("First_workbook address").sheet1.range("A1").value=
workbooks("second_workbook address").sheet1.range("C1").value
then
workbooks("First_workbook address").sheet1.range("A1").colour = vbRed
Endif
solved How to compare two Excel workbook, and if the data matches on both sheet, color code from second should automatically apply to first one [closed]