(* To preserve the current stylesheet information it has to be
plucked out of the StyleDefinitions; 1st time this is OK as the
StyleDefinitions = just a notebook name, but after adding items it
gets messy and we need to extract the stylesheet notebook name to reapply it.
*)
sdef = CurrentValue[EvaluationNotebook[], StyleDefinitions];
If[! StringQ[sdef], (*
  this is typically just the filename of a stylesheet notebook,
  but if it isn't... *)
  sdef = ToString[sdef];
  sdef = StringCases[sdef, "StyleDefinitions -> " ~~ __  ~~ ".nb]]",
    1];
  sdef = StringReplace[
    sdef[[1]], {"StyleDefinitions -> " -> "", "]]" -> ""}]
  ];
SetOptions[EvaluationNotebook[], StyleDefinitions -> Notebook[{
     Cell[StyleData[StyleDefinitions -> sdef]],
     Cell[StyleData["MessageMenuLabel"], Bold,
      FontColor -> RGBColor[N[174/255], 0.1, 0],
      FontSize ->
       CurrentValue[{StyleDefinitions, "Output", "FontSize"}]],
     Cell[StyleData["MessageText"],
      FontColor -> RGBColor[0.1, 0.1, 0.1]]
     }
    ]
  (* last line needed per Kuba's Programming scripts to create and modify stylesheets answer*)
  /. s_Symbol /; Context[s] === "Global`" :>
   Symbol["FrontEnd`" <> SymbolName[s]]]
(* Do something illegal to check the message appearance... *)
1/0