* lisp/minibuffer.el (completions-common-part): Make it blue when possible

etc/NEWS

@@ -409,6 +409,8 @@ matches strings where the pattern appears as a subsequence.  Put
 simply, makes "foo" complete to both "barfoo" and "frodo".  Add 'flex'
 to 'completion-styles' or 'completion-category-overrides' to use it.
 
+** The 'completion-common-part' face is now visible by default.
+
 +++
 ** New face attribute ':extend' to control face extension at EOL.
 The new face attribute ':extend' controls whether to use the face for

lisp/minibuffer.el

@@ -1692,7 +1692,9 @@ See also `display-completion-list'.")
   "Face for the first character after point in completions.
 See also the face `completions-common-part'.")
 
-(defface completions-common-part '((t nil))
+(defface completions-common-part
+  '((((class color) (min-colors 16) (background light)) :foreground "blue3")
+    (((class color) (min-colors 16) (background dark)) :foreground "lightblue"))
   "Face for the parts of completions which matched the pattern.
 See also the face `completions-first-difference'.")