This bug affects printing post-scripts in black and white.

From the documentation of ps-default-fs and ps-default-bg, we get:

> This variable is used only when `ps-print-color-p' (which see) is neither
nil
> nor black-white.

That does not match with the code .. these values affect the postscript
export even when ps-print-color-p is set to 'black-white.

On reviewing the code, the bug was that black-white was written as
back-white (note the typo).

I'll attach the patch in a followup email.

In GNU Emacs 25.1.50.36 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.23)
 of 2016-08-24
Repository revision: 70cfe9df957bd2f0699f62fe5e69176313f7c8f0
Windowing system distributor 'The X.Org Foundation', version 11.0.60900000
System Description: Red Hat Enterprise Linux Workstation release 6.6
(Santiago)


Configured using:
 'configure --with-modules
 --prefix=/home/kmodi/usr_local/apps/6/emacs/master
 'CPPFLAGS=-fgnu89-inline -I/home/kmodi/usr_local/6/include
 -I/usr/include/freetype2 -I/usr/include' 'CFLAGS=-ggdb3 -O0'
 'CXXFLAGS=-ggdb3 -O0' 'LDFLAGS=-L/home/kmodi/usr_local/6/lib
 -L/home/kmodi/usr_local/6/lib64 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK2 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix
-- 

Kaushal Modi