Excel 2003 SP3

have spreadsheet with percentages in cells; some cells have "N/A"; already
using conditional formatting (3 conditions) to change cell background color
for percentages; want background color of cells with "N/A" to remain clear
(white); need a macro that will find cells with "N/A" and change them to an
alternate background color format (overriding the existing conditional
formatting for that cell); if cell changes in future to a percentage, need
the 3 conditions format