title: Changing colours of pixels of plt.imshow() image
body: <p>I need to draw an image with matplotlib's imshow() and then mark some pixels with different colour. Just changing their value in the initial array won't work as I need to use colours not present in the colourmap I am using. So my initial intention was to plot a second generated array above the first image with most of it masked and the required pixels not masked and with some values (potentially different ones to use different colour for different coordinates). And it works nicely with the matplotlib's interactive viewer, but when saving into a file everything gets distorted probably because of this bug, which I reported in the same situation: <a href="https://github.com/matplotlib/matplotlib/issues/3057" rel="noreferrer">https://github.com/matplotlib/matplotlib/issues/3057</a></p>
  
  <p>Are there any other options to change colour of some pixels? </p>