Use black-on-white by default for doc-view-svg-face.

* lisp/doc-view.el (doc-view-svg-face): Define black on white as
default value instead of using the current theme's values.
* etc/NEWS: Adjust entry for doc-view-svg-face.

etc/NEWS

@@ -1544,10 +1544,12 @@ default is non-nil if your system supports display of SVG images.
 ---
 *** New face 'doc-view-svg-face'.
 This replaces 'doc-view-svg-foreground' and 'doc-view-svg-background'.
-If you don't like the colors produced by the default definition of
-this new face when DocView displays documents, customize this face to
-restore the colors you were used to, or to get colors more to your
-liking.
+By default, this face has black foreground on white background and
+inherits from the default face.  When unsetting the foreground and
+background values, the display in DocView is styled according to the
+current theme.  However, this, or any non-standard values, can result in
+poor contrast for documents which aren't simply black text on white
+background.
 
 ---
 *** DocView buffers now display a new tool bar.

lisp/doc-view.el

@@ -238,10 +238,15 @@ showing only titles and no page number."
   :type 'boolean
   :version "29.1")
 
-(defface doc-view-svg-face '((t :inherit default))
+(defface doc-view-svg-face '((t :inherit default
+                                :background "white"
+                                :foreground "black"))
   "Face used for SVG images.
-Only background and foreground colors are used.
-See `doc-view-mupdf-use-svg'."
+See `doc-view-mupdf-use-svg'.
+
+Only background and foreground colors are used as the SVG image's
+descriptors, see (info \"(elisp) SVG Images\").  Non-standard values may
+cause low-contrast issues with certain documents."
   :version "30.1")
 
 (make-obsolete 'doc-view-svg-background 'doc-view-svg-face "30.1")