Re: ps-print-buffer-with-faces doesn't use selected frame's background

[Richard Stallman]

    If the ~/.emacs file have:

        (setq initial-frame-alist (append '((background-color "DarkSlateGray"))
                                          initial-frame-alist))
        (setq default-frame-alist (append '((background-color "DarkSlateGray"))
                                          default-frame-alist))
        (require 'printing) ; or (require 'ps-print)

    then ps-print is loaded before initial-frame-alist has any effect, so, 
    ps-default-bg is set to white.

Yes, that is the cause.  There is no way it can examine a frame
parameter before there is a frame.  So your other approach would seem
to be needed.