There's been some talk about making a "dark mode" for our 2D plotting. I did a bit of investigating with raw.plot(), here's what I found:

• because we specify colors in mne/defaults.py (which gets loaded when the package is imported), using plt.style.use('dark_mode') or with plt.style.context('dark_mode'): don't work as expected unless the import mne statement comes after the style invocation.
• the default cycles don't have enough blue-ish colors to keep things roughly the same as they are now (we currently use 3 different shades of blue for mag, grad, and ref-meg channels).
• there is actually not very good parallelism between MPL normal mode and dark mode. I had wrongly thought that the "blue-orange-green-red..." sequence in default MPL style was replaced in dark mode by pale versions of each color but with roughly the same hue. This is not the case: below are the actual colors (with names made up by me), showing that, e.g. (for C2), what is green in normal mode is lavender in dark mode. This is... not great.

#    |   normal mode     |      dark mode
# ------------------------------------------------
# C0 |  #1f77b4  blue    |  #8dd3c7  pale blue
# C1 |  #ff7f0e  orange  |  #feffb3  pale yellow
# C2 |  #2ca02c  green   |  #bfbbd9  pale lavender
# C3 |  #d62728  red     |  #fa8174  salmon
# C4 |  #9467bd  purple  |  #81b1d2  blue
# C5 |  #8c564b  brown   |  #fdb462  tangerine
# C6 |  #e377c2  pink    |  #b3de69  spring green
# C7 |  #7f7f7f  grey    |  #bc82bd  lavender
# C8 |  #bcbd22  yellow  |  #ccebc4  pale green
# C9 |  #17becf  teal    |  #ffed6f  yellow

See below for what is the best compromise I was able to come up with so far while using the default cycler colors. Obviously this is an incomplete attempt, just wanted to show the blue-and-teal-on-black look:

alternatives

we could roll-our-own dark mode by adding a couple keys to the default color dict (i.e., "foreground" and "background"), and then having a separate pre-defined dict for a dark-mode version of the default colors.

cc @cbrnr, who has expressed interest in this.