I just figured out I can certainly search "G" and "Y" by using "Format"-"Conditional Formatting" like this:

=ISNUMBER(SEARCH("G",AA4)) then make format color=green
=ISNUMBER(SEARCH("Y",AA4)) then make format color=yellow

But I still need to do the rest three colors by VBA. I'm wondering if there is anyway I can do ALL conditions in VBA? Thanks.