Interaction issue between GDSCTools, Reports and Colormap

[Donnyvdm]

I've got an issue when running the test suite of GDSCTools. There are many ways to fix it, but I think the most natural fix is in the colormap package, hence this issue. Feel free to move it to one of the other repos if you think that's more appropriate.

The fix I'm proposing is that the cmap_builder-function should check if there is only one parameter given and it is already a matplotlib cmap, it should simply return that cmap.

A solution would look roughly like this:

from matplotlib.colors import Colormap as MPLColormap
...
def cmap_builder(name, name2=None, name3=None):
    ...
    elif name in c.colormaps:
        return c.cmap(name)
    elif isinstance(name, MPLColormap):   # Proposed addition
        return name                                     

This issue arises from the following code:
In GDCTools.anova_results:

class ANOVAResults(object):
    ....
    def get_html_table(...):
        ....
        cmap_clip = cmap_builder('#ffffff', '#0070FF')
        ...
        html.add_bgcolor(this, cmap_clip, mode='clip', threshold=clip_threshold)

The add_bgcolor comes from reports.HTMLTable class:

    def add_bgcolor(self, colname, cmap='copper', mode='absmax', threshold=2):
        ....
        cmap = cmap_builder(cmap)

So this last cmap_builder gets called with an object that's already a matplotlib colormap.

If you're happy with the above solution, I can submit a PR. If you want to fix it in Reports or GDSCTools, please let me know.