id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
809323722,MDU6SXNzdWU4MDkzMjM3MjI=,4913,plot: ValueError for invalid `hue` argument is confusing,41184617,closed,0,,,2,2021-02-16T13:43:02Z,2021-04-13T11:19:21Z,2021-03-30T16:39:50Z,NONE,,,,"```python
import xarray as xr
xr.DataArray([[1,2,3], [4,5,6]], dims=(""a"", ""b"")).plot(x=""a"", hue=""c"")  # note: it should be hue=""b""
```
**What happened**:
raises

```
ValueError: y must be one of None, 'a', 'b'
```

**What you expected to happen**:

```
ValueError: hue must be one of None, 'a', 'b'
```

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.7 (default, Mar 23 2020, 22:36:06) 
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 3.16.0-4-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_US.utf-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.5
libnetcdf: 4.6.3

xarray: 0.16.2
pandas: 1.2.1
numpy: 1.19.2
scipy: 1.5.2
netCDF4: 1.5.4
pydap: installed
h5netcdf: None
h5py: 2.10.0
Nio: None
zarr: 2.6.1
cftime: 1.3.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.0
cfgrib: None
iris: None
bottleneck: None
dask: 2021.01.1
distributed: 2021.01.1
matplotlib: 3.3.2
cartopy: 0.18.0
seaborn: 0.11.1
numbagg: None
pint: 0.16.1
setuptools: 52.0.0.post20210125
pip: 20.3.3
conda: 4.9.2
pytest: 6.2.2
IPython: 7.20.0
sphinx: 3.4.3


</details>
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/4913/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue