mand[c_Complex, max_Integer:100] :=Module[ {z=c},Do[If[Abs[z]>4, Return[i]]; z = z^2 + c,{i,max}]]

bn=Table[
Table[
mand[x+y I],
{x, -1.3, 0.8, 0.005}
],
{y, -1, 1, 0.005}
];

Manipulate[ArrayPlot[bn,ColorFunction->(Hue[Mod[#+a,1]]&),ColorFunctionScaling->True],{a,1,20}]