Szabolcs code Excel like conditional formatting matrix

(*start*)
Clear[g1, g2, nn]
nn = 32;
a = Array[
   Function[n,
    1/Plus @@ Map[#*MoebiusMu[#]/EulerPhi[#] &, Divisors[n]]], nn];
g1 = Graphics[
   ArrayPlot[
    Table[Table[a[[GCD[nn - n + 1, k]]], {k, 1, nn}], {n, 1, nn}],
    ColorFunction -> "TemperatureMap", Frame -> False]];
g2 = Graphics[
   Table[Table[
     Rotate[Text[Style[a[[GCD[n, k]]], Black], {n - 1/2, k - 1/2}],
      Pi/2], {k, 1, nn}], {n, 1, nn}]];
g3 = Rotate[Show[g1, g2, ImageSize -> Large], -Pi/2];
g3
(*end*)

(* szabolcs code from chat room at Mathematica stackexchange \
14.1.2018 *)
Clear[a, matrix, nn]
nn = 32;
a = Array[
   Function[n,
    1/Plus @@ Map[#*MoebiusMu[#]/EulerPhi[#] &, Divisors[n]]], nn];
matrix = Reverse[Table[a[[GCD[n, k]]], {k, 1, nn}, {n, 1, nn}], 2];
MatrixPlot[Transpose[matrix], DataReversed -> True,
 ColorFunction -> "GrayYellowTones", Frame -> False,
 PlotRangePadding -> None,
 Epilog -> MapIndexed[Text[#1, #2 - 1/2] &, matrix, {2}]]
(*end*)