A different color appears in the unused screen lines

[Richard Stallman]

When I put this in .emacs

(custom-set-faces
  ;; custom-set-faces was added by Custom -- don't edit or cut/paste it!
  ;; Your init file should contain only one such instance.
 '(default ((t (:stipple nil :background "DarkSlateGray" :foreground "wheat" 
:inverse-video nil :box nil :strike-through nil :overline nil :underline nil 
:slant normal :weight normal :height 135 :width normal :family 
"adobe-courier")))))

the specified colors appear, but empty areas of the screen--those
beyond the last character on the line or in the buffer--come out in a
different color, a little lighter than DarkSlateGray.

I did M-x list-faces-display, and I saw that no face had a background
equivalent to the color of those empty areas.

I tried substituting a couple of other background colors.  I tried
"black" and "blue".  In those cases, the problem did not happen:
the screen appeared black or blue down to the end.

Does anyone know where that color is coming from?  I tried to study
the display code to figure it out but I can't find it.  I suspect that
the cause has to do with what GC is specified when x_clear_end_of_line
runs; does anyone know where that is specified?