howto define dynamic color with gnus-summary-line-format

[haomiao]

Hi
      I want gnus can display different color according to some
dynamic condition in my summary buffer,
  for example
         if  date of mail is today, then  the date color is red
         else the date color is blue
      How can I get that effect, by setting gnus-summary-line-format
or something else?

      My current gnus-summary-line-format is
             (setq gnus-summary-line-format "%U%R%z %3{%uc%}: %1{%B
%-23,23n%} %s\n")

      I am using GNU Emacs 22.1.1 (i386-mingw-nt5.1.2600) and my gnus
is 5.10.8.