The slrn newsreader has an attractive interface with different colours for the author, subject and date columns when browsing list of articles in a newsgroup. I am looking for the Emacs font/face variables for these fields in gnus, but have not been able to find them. The gnus manual for faces does not list the available faces and none of the faces list in Emacs (M-x customize-face gnus-... looks relevant. I am using gnus 5.13 in Emacs 23.2.1.
(This question is not related to displaying "faces" (icons/avatars) in Emacs or gnus.)
Solved: See my answer below.
The format string for various elements in gnus can be customized by modifying the appropriate variable. The variable for the summary line is gnus-summary-format-line. I am not using the default value for this variable, but instead am using the value %U%R%z %(%&user-date; %-15,15f %* %B%s%)\n.
As described here, a new face can be applied to any (sub)section of a format line by bracketing the section with %1{ and %}, where the 1 in this example corresponds to gnus-face-1. gnus-face-1 in my installation defaults to "italics", so adding the following to my ~/.emacs file results in the author in the summary line appearing in italics:
(setq gnus-summary-line-format "%U%R%z %(%&user-date; %1{%-15,15f%} %* %B%s%)\n")