Remove diff-added, diff-changed and diff-removed annoying backgrounds.

  Two reasons:
    1) With background, diffs are more difficult to read.

    2) In magit buffers, where highlighting is used to emphasize the current
    chunk, current chunk actually becomes less highlighted. During movement
    between chunks everything blinks

solarized.el

@@ -303,9 +303,9 @@
      `(custom-state ((,class (:foreground ,green))))
 
      ;; diff
-     `(diff-added ((,class (:foreground ,green))))
-     `(diff-changed ((,class (:foreground ,yellow))))
-     `(diff-removed ((,class (:foreground ,red))))
+     `(diff-added ((,class (:foreground ,green :background ,solarized-bg))))
+     `(diff-changed ((,class (:foreground ,yellow :background ,solarized-bg))))
+     `(diff-removed ((,class (:foreground ,red :background ,solarized-bg))))
      `(diff-header ((,class (:background ,solarized-bg))))
      `(diff-file-header
        ((,class (:background ,solarized-bg :foreground ,solarized-fg :weight bold))))