`:bone` colormap seems wrong

[asinghvi17]

Here, the bone colormap is a straight grayscale white-to-black map, but Matplotlib gives it a blue tinge.

_bone_data = {'red':   ((0., 0., 0.),
                        (0.746032, 0.652778, 0.652778),
                        (1.0, 1.0, 1.0)),
              'green': ((0., 0., 0.),
                        (0.365079, 0.319444, 0.319444),
                        (0.746032, 0.777778, 0.777778),
                        (1.0, 1.0, 1.0)),
              'blue':  ((0., 0., 0.),
                        (0.365079, 0.444444, 0.444444),
                        (1.0, 1.0, 1.0))}

Is there a particular reason we sampled the colormaps here and did not translate Matplotlib's colormaps directly?

[cormullion]

Yes, for some reason back in the day there must have been a name-clash, so it looks like the Matplotlib 'bone' got renamed as 'bone_1'.