Random gray color. How to do?

I have a 30 random boxes at the images, but I need to do a boxes in random gray color. How to do it?

patch(idx(i)+R(:,1),idy(i)+R(:,2),'k')

What I should write instead of 'k'?

Answer 1

[Image Analyst]

Or you can do the easier method like I suggested to you here in this link where you just burn the color into the image.