Make title separator independently customizable from progress bar

beamercolorthememetropolis.sty

@@ -76,9 +76,11 @@
 \setbeamercolor{progress bar}{%
   use=alerted text,
   fg=alerted text.fg,
-  bg=mDarkTeal!50
+  bg=normal text.bg!50!fg
 }
 
+\setbeamercolor{title separator}{use=progress bar, parent=progress bar}
+
 \setbeamercolor{palette primary}{%
   % The “primary” palette should be used for the most important navigational
   % elements, and possibly of other elements.

beamerthemem.sty

@@ -170,7 +170,8 @@
     \fi
 
     \begin{tikzpicture}
-      \draw[alerted text.fg] (0, 0) -- (\textwidth, 0);
+      \usebeamercolor{title separator}
+      \draw[fg] (0, 0) -- (\textwidth, 0);
     \end{tikzpicture}%
     \vspace*{1em}%