Clear[mbrotColor]
mbrotColor[c_Complex] := Module[{max = 100, r},
  r = NestWhile[{#[[1]] + 1, #[[2]]^2 + c} &,
     {0, c}, Norm[#[[2]]] < 2 &, 1, max][[1]];
  1.0 - ((max - r)/max)^2]
DistributeDefinitions[mBrotColor]
With[{granularity = 0.004},
 ArrayPlot[Transpose[ParallelTable[mbrotColor[i + j I],
    {i, -2, 0.75, granularity}, {j, -1, 1, granularity}]],
  ImageSize -> 450]]