How to redefine a color for a specific value in a matplotlib colormap

Question

I want to use the colormap rainbow in an image using imshow. It works perfectly, but I want to redefine the color for the value 0. Ins

Answer 1

You can also use set_under which I think makes more semantic sense than using set_bad

my_cmap = matplotlib.cm.get_cmap('rainbow')
my_cmap.set_under('w')
imshow(np.arange(25).reshape(5, 5),
       interpolation='none',
       cmap=my_cmap,
       vmin=.001)

You can tweak the colorbar to also show the 'under' (and the symmetric 'over') color using the kwarg extend, see example and docs.

For an answer to a duplicate with more complete examples see How to create matplotlib colormap that treats one value specially?