CurrentValue[$FrontEndSession, {AutoStyleOptions, "SymbolContextStyles", $Context}] = Purple;

SetOptions[$FrontEnd,
 NotebookEventActions :> {
   {"MenuCommand", "New"} :> CreateDocument[
     ExpressionCell[
       Defer[
         CurrentValue[$FrontEndSession, {AutoStyleOptions, "SymbolContextStyles", $Context}] = Purple
       ]
     , "Code"]
     ]
   }
 , CellContext -> Notebook
 ]