Issues with using custom matplotlib colormap

I'm having two issues:

1. When using `xarray.hvplot.quadmesh`, I'm unable to use a a custom `LinearSegmentedColormap` unless I register it with with matplotlib and call it that way.




2. I'm able to use a custom registered matplotlib colormap in one of my conda environments (running Python 3.10.5), but not the other (running Python 3.8.13). This is the same exact code as successfully plotted above:


```
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/IPython/core/formatters.py:973, in MimeBundleFormatter.__call__(self, obj, include, exclude)
970 method = get_real_method(obj, self.print_method)
972 if method is not None:
--> 973 return method(include=include, exclude=exclude)
974 return None
975 else:

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/core/dimension.py:1294, in Dimensioned._repr_mimebundle_(self, include, exclude)
1287 def _repr_mimebundle_(self, include=None, exclude=None):
1288 """
1289 Resolves the class hierarchy for the class rendering the
1290 object using any display hooks registered on Store.display
1291 hooks. The output of all registered display_hooks is then
1292 combined and returned.
1293 """
-> 1294 return Store.render(self)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/core/options.py:1426, in Store.render(cls, obj)
1424 data, metadata = {}, {}
1425 for hook in hooks:
-> 1426 ret = hook(obj)
1427 if ret is None:
1428 continue

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/ipython/display_hooks.py:277, in pprint_display(obj)
275 if not ip.display_formatter.formatters['text/plain'].pprint:
276 return None
--> 277 return display(obj, raw_output=True)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/ipython/display_hooks.py:253, in display(obj, raw_output, **kwargs)
251 elif isinstance(obj, (HoloMap, DynamicMap)):
252 with option_state(obj):
--> 253 output = map_display(obj)
254 elif isinstance(obj, Plot):
255 output = render(obj)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/ipython/display_hooks.py:141, in display_hook..wrapped(element)
139 try:
140 max_frames = OutputSettings.options['max_frames']
--> 141 mimebundle = fn(element, max_frames=max_frames)
142 if mimebundle is None:
143 return {}, {}

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/ipython/display_hooks.py:201, in map_display(vmap, max_frames)
198 max_frame_warning(max_frames)
199 return None
--> 201 return render(vmap)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/ipython/display_hooks.py:68, in render(obj, **kwargs)
65 if renderer.fig == 'pdf':
66 renderer = renderer.instance(fig='png')
---> 68 return renderer.components(obj, **kwargs)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/renderer.py:398, in Renderer.components(self, obj, fmt, comm, **kwargs)
395 embed = (not (dynamic or streams or self.widget_mode == 'live') or config.embed)
397 if embed or config.comms == 'default':
--> 398 return self._render_panel(plot, embed, comm)
399 return self._render_ipywidget(plot)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/renderer.py:405, in Renderer._render_panel(self, plot, embed, comm)
403 doc = Document()
404 with config.set(embed=embed):
--> 405 model = plot.layout._render_model(doc, comm)
406 if embed:
407 return render_model(model, comm)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/viewable.py:505, in Renderable._render_model(self, doc, comm)
503 if comm is None:
504 comm = state._comm_manager.get_server_comm()
--> 505 model = self.get_root(doc, comm)
507 if config.embed:
508 embed_state(self, model, doc,
509 json=config.embed_json,
510 json_prefix=config.embed_json_prefix,
511 save_path=config.embed_save_path,
512 load_path=config.embed_load_path,
513 progress=False)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/viewable.py:556, in Renderable.get_root(self, doc, comm, preprocess)
539 """
540 Returns the root model and applies pre-processing hooks
541
(...)
553 Returns the bokeh model corresponding to this panel object
554 """
555 doc = init_doc(doc)
--> 556 root = self._get_model(doc, comm=comm)
557 if preprocess:
558 self._preprocess(root)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/layout/base.py:146, in Panel._get_model(self, doc, root, parent, comm)
144 if root is None:
145 root = model
--> 146 objects = self._get_objects(model, [], doc, root, comm)
147 props = dict(self._init_params(), objects=objects)
148 model.update(**self._process_param_change(props))

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/layout/base.py:131, in Panel._get_objects(self, model, old_objects, doc, root, comm)
129 else:
130 try:
--> 131 child = pane._get_model(doc, root, model, comm)
132 except RerenderError:
133 return self._get_objects(model, current_objects[:i], doc, root, comm)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/pane/holoviews.py:265, in HoloViews._get_model(self, doc, root, parent, comm)
263 plot = self.object
264 else:
--> 265 plot = self._render(doc, comm, root)
267 plot.pane = self
268 backend = plot.renderer.backend

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/panel/pane/holoviews.py:342, in HoloViews._render(self, doc, comm, root)
339 if comm:
340 kwargs['comm'] = comm
--> 342 return renderer.get_plot(self.object, **kwargs)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/bokeh/renderer.py:70, in BokehRenderer.get_plot(self_or_cls, obj, doc, renderer, **kwargs)
63 @bothmethod
64 def get_plot(self_or_cls, obj, doc=None, renderer=None, **kwargs):
65 """
66 Given a HoloViews Viewable return a corresponding plot instance.
67 Allows supplying a document attach the plot to, useful when
68 combining the bokeh model with another plot.
69 """
---> 70 plot = super().get_plot(obj, doc, renderer, **kwargs)
71 if plot.document is None:
72 plot.document = Document() if self_or_cls.notebook_context else curdoc()

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/renderer.py:240, in Renderer.get_plot(self_or_cls, obj, doc, renderer, comm, **kwargs)
237 defaults = [kd.default for kd in plot.dimensions]
238 init_key = tuple(v if d is None else d for v, d in
239 zip(plot.keys[0], defaults))
--> 240 plot.update(init_key)
241 else:
242 plot = obj

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/plot.py:949, in DimensionedPlot.update(self, key)
947 if len(self) == 1 and ((key == 0) or (key == self.keys[0])) and not self.drawn:
948 return self.initialize_plot()
--> 949 item = self.__getitem__(key)
950 self.traverse(lambda x: setattr(x, '_updated', True))
951 return item

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/plot.py:432, in DimensionedPlot.__getitem__(self, frame)
430 if isinstance(frame, int) and frame > len(self):
431 self.param.warning("Showing last frame available: %d" % len(self))
--> 432 if not self.drawn: self.handles['fig'] = self.initialize_plot()
433 if not isinstance(frame, tuple):
434 frame = self.keys[frame]

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/geoviews/plotting/bokeh/plot.py:111, in GeoPlot.initialize_plot(self, ranges, plot, plots, source)
109 def initialize_plot(self, ranges=None, plot=None, plots=None, source=None):
110 opts = {} if isinstance(self, HvOverlayPlot) else {'source': source}
--> 111 fig = super(GeoPlot, self).initialize_plot(ranges, plot, plots, **opts)
112 if self.geographic and self.show_bounds and not self.overlaid:
113 from . import GeoShapePlot

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/bokeh/element.py:1397, in ElementPlot.initialize_plot(self, ranges, plot, plots, source)
1394 self.handles['y_range'] = plot.y_range
1395 self.handles['plot'] = plot
-> 1397 self._init_glyphs(plot, element, ranges, source)
1398 if not self.overlaid:
1399 self._update_plot(key, plot, style_element)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/bokeh/element.py:1341, in ElementPlot._init_glyphs(self, plot, element, ranges, source)
1339 else:
1340 style = self.style[self.cyclic_index]
-> 1341 data, mapping, style = self.get_data(element, ranges, style)
1342 current_id = element._plot_id
1344 with abbreviated_exception():

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/geoviews/plotting/bokeh/plot.py:171, in GeoPlot.get_data(self, element, ranges, style)
169 if self._project_operation and self.geographic:
170 element = self._project_operation(element, projection=self.projection)
--> 171 return super(GeoPlot, self).get_data(element, ranges, style)

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/bokeh/raster.py:90, in RasterPlot.get_data(self, element, ranges, style)
88 mapping = dict(image='image', x='x', y='y', dw='dw', dh='dh')
89 val_dim = element.vdims[0]
---> 90 style['color_mapper'] = self._get_colormapper(val_dim, element, ranges, style)
91 if 'alpha' in style:
92 style['global_alpha'] = style['alpha']

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/bokeh/element.py:1913, in ColorbarPlot._get_colormapper(self, eldim, element, ranges, style, factors, colors, group, name)
1908 if isinstance(cmap, list) and len(cmap) != ncolors:
1909 raise ValueError('The number of colors in the colormap '
1910 'must match the intervals defined in the '
1911 'color_levels, expected %d colors found %d.'
1912 % (ncolors, len(cmap)))
-> 1913 palette = process_cmap(cmap, ncolors, categorical=categorical)
1914 if isinstance(self.color_levels, list):
1915 palette, (low, high) = color_intervals(palette, self.color_levels, clip=(low, high))

File /storage/work/cnd5285/miniconda/envs/uviz/lib/python3.8/site-packages/holoviews/plotting/util.py:911, in process_cmap(cmap, ncolors, provider, categorical)
909 palette = colorcet_cmap_to_palette(cmap, ncolors, categorical)
910 else:
--> 911 raise ValueError("Supplied cmap %s not found among %s colormaps." %
912 (cmap,providers_checked))
913 else:
914 try:
915 # Try processing as matplotlib colormap

ValueError: Supplied cmap FLUT CIMSS not found among matplotlib, bokeh, or colorcet colormaps.
```

Successful environment (Python 3.10.5):
```
bokeh 2.4.3 py310hff52083_0 conda-forge
holoviews 1.14.9 pyhd8ed1ab_0 conda-forge
hvplot 0.8.1 py_0 pyviz
```

Failed environment (Python 3.8.13):
```
bokeh 2.4.3 pyhd8ed1ab_3 conda-forge
holoviews 1.15.1 py_0 pyviz
hvplot 0.8.1 py_0 pyviz
```