issues: 894819396

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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
894819396 MDU6SXNzdWU4OTQ4MTkzOTY= 5337 `colors` in Dataset plot methods 15079414 open 0     2 2021-05-18T22:01:48Z 2021-07-04T01:12:45Z   CONTRIBUTOR      

While working on the plot method docstrings (#5285), I (and @keewis) found that the colors kwarg for the Dataset plot methods is not as useful as it could be. In some cases it is silently ignored (warning or error could be raised instead).

For Dataset.plot.scatter, I think it would make sense for a list of colors to be able to be passed to be used for discrete hue_style. Currently, the only way you can control these for discrete hue_style is if hue is numeric and you also pass levels.

My original notes on Dataset.plot.scatter: Yeah, it seems like the `colors` argument is not used in `ds.plot.scatter`. But no error is raised, `colors` is just silently dropped (`ax.scatter` would raise `AttributeError` if it weren't) in most cases. I did find that you can get the marker colors to change by passing `color` or `c` with a discrete `hue_style`. ```python import xarray as xr import numpy as np ds = xr.tutorial.scatter_example_dataset() ds["c"] = (ds.A.dims, np.random.choice(("r", "g", "b"), ds.A.shape)) ds.plot.scatter("A", "B", hue="c", c=(0, 0, 0)) # works but prints (doesn't raise) warning ds.plot.scatter("A", "B", hue="c", color=(0, 0, 0)) # works ``` However, if you have a continuous `hue_style`, passing `c` is ignored (since this is done internally), and passing `color` raises `ValueError` since it conflicts with `c`. It seems like at the moment, `colors` is really only intended to be used with contour(f) for levels, like how it is in Matplotlib. Maybe in the future it could be used to allow passing colors to be used in the color cycle for discrete `hue_style`, but it doesn't currently do that. So for now, maybe in the docstring we should note this current behavior (doing nothing or raising error). ~~`levels` is also unused in `_dsplot` functions, maybe could be removed~~ actually I was able to get `colors` to sort of work with discrete `hue_style` by also providing `levels`, but `levels` only makes sense for numeric type: ```python ds["c2"] = (ds.A.dims, np.random.choice((1, 2, 3), ds.A.shape)) ds.plot.scatter("A", "B", hue="c2", colors=["r", "g", "b"], levels=[1, 2, 3, 4]) # works (rgb) ds.plot.scatter("A", "B", hue="c2", hue_style="discrete", colors=["r", "g", "b"]) # `colors` does nothing ``` _Originally posted by @zmoon in https://github.com/pydata/xarray/pull/5285#discussion_r632986368_ 
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