76:  Why does Emacs ignore my X resources (my .Xdefaults file)?

  As of version 19, Emacs searches for X resources in the files specified
  by the XFILESEARCHPATH, XUSERFILESEARCHPATH, and XAPPLRESDIR environment
  variables, emulating the functionality provided by programs written using
  Xt.

  XFILESEARCHPATH and XUSERFILESEARCHPATH should be a list of file names
  separated by colons; XAPPLRESDIR should be a list of directory names
  separated by colons.

  Emacs searches for X resources
 
    + specified on the command line, with the "-xrm RESOURCESTRING"
      option,
    + then in the value of the XENVIRONMENT environment variable,
      - or if that is unset, in the file named ~/.Xdefaults-HOSTNAME if it
        exists
        (where HOSTNAME is the hostname of the machine Emacs is running on),
    + then in the screen-specific and server-wide resource properties
      provided by the server,
      - or if those properties are unset, in the file named ~/.Xdefaults
        if it exists,
    + then in the files listed in XUSERFILESEARCHPATH,
      - or in files named LANG/Emacs in directories listed in XAPPLRESDIR
        (where LANG is the value of the LANG environment variable), if
        the LANG environment variable is set,
      - or in files named Emacs in the directories listed in XAPPLRESDIR
      - or in ~/LANG/Emacs (if the LANG environment variable is set),
      - or in ~/Emacs,
    + then in the files listed in XFILESEARCHPATH.