Enhance spherical tracer transport test viz

docs/developers_guide/framework/visualization.md

@@ -154,7 +154,13 @@ colormap).
 
 The `colorbar_limits` are the lower and upper bound of the colorbar range.
 
+There are also two optional config options used to set the colors on either end of the colormap:
 
+```cfg
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+```
 ### plotting from lat/lon grids
 
 You can use {py:func}`polaris.viz.plot_global_lat_lon_field()` to plot a field 

docs/developers_guide/ocean/tasks/correlated_tracers_2d.md

@@ -77,6 +77,10 @@ each resolution.  The colormap is controlled by these options:
 # colormap
 colormap_name = viridis
 
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+
 # the type of norm used in the colormap
 norm_type = linear
 

docs/developers_guide/ocean/tasks/divergent_2d.md

@@ -71,6 +71,10 @@ each resolution.  The colormap is controlled by these options:
 # colormap
 colormap_name = viridis
 
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+
 # the type of norm used in the colormap
 norm_type = linear
 

docs/developers_guide/ocean/tasks/nondivergent_2d.md

@@ -77,6 +77,10 @@ each resolution.  The colormap is controlled by these options:
 # colormap
 colormap_name = viridis
 
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+
 # the type of norm used in the colormap
 norm_type = linear
 

docs/developers_guide/ocean/tasks/rotation_2d.md

@@ -71,6 +71,10 @@ each resolution.  The colormap is controlled by these options:
 # colormap
 colormap_name = viridis
 
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+
 # the type of norm used in the colormap
 norm_type = linear
 

polaris/ocean/tasks/sphere_transport/sphere_transport.cfg

@@ -84,6 +84,10 @@ slotted_cylinders_amplitude = 1.0
 # colormap
 colormap_name = viridis
 
+# [optional] colormap set_under and set_over options
+under_color = k
+over_color = orange
+
 # the type of norm used in the colormap
 norm_type = linear
 

polaris/viz/spherical.py

@@ -9,6 +9,7 @@
 import matplotlib.colors as cols
 import matplotlib.pyplot as plt
 import uxarray as ux
+from matplotlib import cm
 from mpl_toolkits.axes_grid1.inset_locator import inset_axes
 from pyremap.descriptor.utility import interp_extrap_corner
 
@@ -81,6 +82,13 @@ def plot_global_mpas_field(mesh_filename, da, out_filename, config,
     projection = cartopy.crs.PlateCarree(central_longitude=central_longitude)
 
     colormap = config.get(colormap_section, 'colormap_name')
+    cmap = cm.get_cmap(colormap)
+    if config.has_option(colormap_section, 'under_color'):
+        under_color = config.get(colormap_section, 'under_color')
+        cmap.set_under(under_color)
+    if config.has_option(colormap_section, 'over_color'):
+        over_color = config.get(colormap_section, 'over_color')
+        cmap.set_over(over_color)
 
     norm_type = config.get(colormap_section, 'norm_type')
     if norm_type == 'linear':
@@ -94,7 +102,7 @@ def plot_global_mpas_field(mesh_filename, da, out_filename, config,
                                      dtype=float)
 
     plot = gdf_data.hvplot.polygons(
-        c=da.name, cmap=colormap, logz=logz,
+        c=da.name, cmap=cmap, logz=logz,
         clim=tuple(colorbar_limits),
         clabel=colorbar_label,
         width=1600, height=800, title=title,