How to set 0 to white at a uneven color ramp

Question

I have an uneven color ramp and I want the 0 to be white. All negative colors have to be bluish and all positive colors have to be reddish. My current attempted displays the 0 bluish and the 0.7 white.

Is there anyway to set the 0 to white?

import numpy as np
import matplotlib.colors as colors 
from matplotlib import pyplot as m

bounds_min = np.arange(-2, 0, 0.1)
bounds_max = np.arange(0, 4.1, 0.1)
bounds = np.concatenate((bounds_min, bounds_max), axis=None)       
norm = colors.BoundaryNorm(boundaries=bounds, ncolors=256)      # I found this on the internet and thought this would solve my problem. But it doesn't...
m.pcolormesh(xx, yy, interpolated_grid_values, norm=norm, cmap='RdBu_r')

Answer 1

The other answer makes it a little more complicated than it needs to be. In order to have the middle point of the colormap at 0, use a DivergingNorm with vcenter=0.

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import DivergingNorm

x, y = np.meshgrid(np.linspace(0,50,51), np.linspace(0,50,51))
z = np.linspace(-2,4,50*50).reshape(50,50)

norm = DivergingNorm(vmin=z.min(), vcenter=0, vmax=z.max())
pc = plt.pcolormesh(x,y,z, norm=norm, cmap="RdBu_r")
plt.colorbar(pc)

plt.show()

Note: From matplotlib 3.2 onwards DivergingNorm will be renamed to TwoSlopeNorm