title: Green-red colormap in matplotlib
body: <p>I have data I want to display using plt.imshow(), using red shades for positive values and green shades for negative values, with a sharp transition from green to red at zero, so it is easy to see whether values are positive or negative. The closest I have found in matplotlib's built-in colormaps is 'PiYG', but this displays purple rather than red, and I'd prefer a sharper transition at the point where the colours change, without the yellowish shades. Do you know of a way to get a good colormap with the properties that I want?</p>