DynamicModule

DynamicModule[{color = RGBColor[0, 0, 0], CellChangeTime, cell},
  CellPrint[cell = Cell[BoxData[""], "Input", Background -> Dynamic[color],
     Evaluatable -> True, CellEvaluationFunction -> Function[
       CellChangeTime = CellChangeTimes /. Cases[
          Cell, Rule[a_, b_] -> Rule[a, b]
          ];
       color = RGBColor[1, 1, 1];
       ]]
   ];
  Refresh[
   If[Not[boxData == recent],(*
    the following doesn't work for comparison *)
    color = Lighter[Gray, 0.7];
    , Null], UpdateInterval -> 1];
  ];