How to make a region of the colorbar completely transparent?

Hello,

I was wondering if I could make a region of my colorbar be completely transparent. Here is a snippet of my code:

    newmap = jet(256);
    ncol = size(newmap,1);
    for n = 129:180
        zpos = n;
        newmap(zpos,:) = [1 1 1];
    end
    colormap(newmap);

Instead of making the region of my colorbar from 129:180 white ([1 1 1]) is there a way to make it transparent? I can set an alpha to the overall plot but that would not make the white completely transparent. I also tried newmap(zpos,:) = 'none'; which did not work. Thank you!