[Python] Is there a cmap which goes from transparant to black (or any other color)?

I'm using the following cmap="binary" on a datasets with zeros and ones. The cmap goes from white to black. This results in the following figure:

Black and white figure:



Because I want to overlap this graph with an existing graph, I want to keep the black but make the white transparant.

Overlapping image with white:



Is there a cmap which goes from transparancy to black ?

I'm using the following code to plot the graphs:

plt.pcolor(mp1,cmap="binary",alpha=0.5)

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