Greyscale spectrograms from MIRToolbox

I am using the excellent MIRToolbox for Matlab for a lot of sound analysis applications these days. It meets a lot of my needs, but there are a few things that I miss. Perhaps the most important one is the ability to make clean greyscale spectrograms. The regular mirspectrum function returns a colour spectrogram with lots of garnish, like this:

Such a spectrogram may be useful in some contexts, but not always. Often I just want a plain, greyscale spectrogram, like this:

Here is my trick to do this, based on mirspectrum:

a=miraudio('myfile.wav');

as=mirspectrum(a, 'Frame', 'Max', 3000);

asm=mirgetdata(as);

figure;

imagesc(asm);

axis xy;

lgrays=zeros(100,3);

for i=1:100

   lgrays(i,:) = 1-i/100;

end

colormap(lgrays);

set(gca,'XTick',[]);

set(gca,'YTick',[]);

Let me know if you have a better solution for doing this.