Spike Viewer Colors

[kohl-carmen]

In the spike viewer, the same shades of red and green are used in the input histograms and to show the spiking of the pyramidal cells. This leads to confusion since it looks like the histograms summarise the internal spiking rate rather than the external drive.
Stephanie suggested to change the pyramidal spikes to shades of blue and cyan since we use blue to show pyramidal neurons in the model schematics.
It might also be useful to change the background color from black to white.
Thanks :)

[blakecaldwell]

A good opportunity to address this would be jonescompneurolab/hnn-core#186