* net/shr.el (shr-colorize-region):

Don't do it on a system not supporting 256 above colors (bug#21557).

lisp/net/shr.el

@@ -1042,7 +1042,7 @@ ones, in case fg and bg are nil."
                (shr-color-visible bg fg)))))))
 
 (defun shr-colorize-region (start end fg &optional bg)
-  (when (or fg bg)
+  (when (and (or fg bg) (>= (display-color-cells) 256))
     (let ((new-colors (shr-color-check fg bg)))
       (when new-colors
 	(when fg