matplotlib - How to create a heat map in python that ranges from green to red?

Question

I'm trying to plot log ratios from the range -3 to 3 and want negative ratios to be green and positive to be red, with a log ratio of 0 (center) to be white in color. None of the pre-existing color schemes in matplotlib provide this option, and I haven't been able to figure out how to output a nice gradient manually.

Answer 1

Using matplotlib.colors.LinearSegmentedColormap's from_list method seems more intuitive than some of the other answers here.

from  matplotlib.colors import LinearSegmentedColormap
cmap=LinearSegmentedColormap.from_list('rg',["r", "w", "g"], N=256) 

Or for more sophisticated tuning:

from  matplotlib.colors import LinearSegmentedColormap
c = ["darkred","red","lightcoral","white", "palegreen","green","darkgreen"]
v = [0,.15,.4,.5,0.6,.9,1.]
l = list(zip(v,c))
cmap=LinearSegmentedColormap.from_list('rg',l, N=256)