The colors of the cake are determined by the color palette of the axis. Therefore, define a matrix with as many rows as the number of cliches for the pie, and use it as a color. The first color refers to the first value ( a), etc.
:
pie([3 2 4 1])
colormap([1 0 0; %
0 1 0; %
0 0 1; %
.5 .5 .5]) %
