Can't get colorbar centered on contorf plot

[sgofferj]

Hi there,

beginner here. I'm trying to get a colorbar centered on 0 on an asymmetric scale. Here's the essence of what I have:

cmap = cm.RdBu
cbar_kwargs = {'label':'m²/s²', 'shrink':0.85, 'aspect':25}
dar.plot.contourf(transform=ccrs.PlateCarree(),cmap=cmap,cbar_kwargs=cbar_kwargs,vmin=-200,vmax=1000,levels=121,center=0)

What I get is this:

Shouldn't center=0 put the center, i.e. the white area, at zero of the colorbar?
How do I get it there?