cmap.set_under() does not work as expected #3590
Description
When using matplotlib, the set_under() method can be used to set values below the range of a colormap to a certain color, for example
import matplotlib
from matplotlib import pyplot
import numpy
dat = numpy.linspace(0, 1)[numpy.newaxis, :]*numpy.linspace(0, 1)[:, numpy.newaxis]
cmap = matplotlib.cm.viridis
#cmap.set_under('w')
pyplot.contourf(dat, vmin=.3, cmap=cmap)
pyplot.colorbar()
pyplot.show()
produces
while uncommenting the cmap.set_under() call produces
However, using xarray to do the same thing,
import matplotlib
from matplotlib import pyplot
from xarray import DataArray
import numpy
da = DataArray(numpy.linspace(0, 1)[numpy.newaxis, :]*numpy.linspace(0, 1)[:, numpy.newaxis])
cmap = matplotlib.cm.viridis
cmap.set_under('w')
da.plot.contourf(vmin=.3, cmap=cmap)
pyplot.show()
produces
where it seems the call to cmap.set_under('w') had no effect. Expected behaviour would be output like the second plot.
Output of xr.show_versions()
Details
In [2]: xarray.show_versions()
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.9 (default, Nov 7 2019, 10:44:02)
[GCC 8.3.0]
python-bits: 64
OS: Linux
OS-release: 5.0.0-37-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: 1.10.0
libnetcdf: 4.6.0
xarray: 0.14.1
pandas: 0.24.2
numpy: 1.16.3
scipy: 1.2.1
netCDF4: 1.3.1
pydap: None
h5netcdf: None
h5py: 2.9.0
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2.1.0
distributed: None
matplotlib: 3.1.1
cartopy: None
seaborn: None
numbagg: None
setuptools: 41.0.1
pip: 19.3.1
conda: None
pytest: 4.4.1
IPython: 7.6.1
sphinx: None