These pics compare images produced by Matlab and by Octave+Gnuplot.

The m-code to produce these is below.

v = ver;
prog = v(1).Name;
map = colormap(jet(65));
pcolor([1 2; 3 3])
shading interp
for n = [1, 4, 16]
colormap (map(1:n:end,:))
print('-dpng', sprintf('%s%d.png',prog,round(64/n)));
end