org-agenda-day-face-function

org-agenda-day-face-function is a variable defined in `org-agenda.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
Function called to determine what face should be used to display a day.
The only argument passed to that function is the day. It should
returns a face, or nil if does not want to specify a face and let
the normal rules apply.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.