% generate data:
x = randn( 1, 100000 );

% histogram:
[h,b] = hist( x, 100 );
% normalize:
bs = b(2)-b(1);
h = h/sum(h)/bs;

% plot:
bar( b, h );
xlabel( 'x' );

% median, quartile:
q = quartiles( x );
%q = quantile( x, [0.25, 0.5, 0.75 ] );

% plot:
hold on;
bar( b(b<q(1)), h(b<q(1)), 'FaceColor', [0.5 0 0.5] );
bar( b((b>=q(1)) & (b<q(2))), h((b>=q(1)) & (b<q(2))), 'FaceColor', [0.9 0 0] );
bar( b((b>=q(2)) & (b<q(3))), h((b>=q(2)) & (b<q(3))), 'FaceColor', [0 0 0.9] );
bar( b(b>=q(3)), h(b>=q(3)), 'FaceColor', [0.5 0 0.5] );
hold off;