Switch default color to lightblue for document theme

[banesullivan]

The default tan color for the document theme has fallen out of my favor and IMO looks dated -- it's time we freshen things up, and this times well with the defaule theme changing to be Document in #4516

Some history: the original tan color was chosen somewhat arbitrarily in 4583baf and was first orange in a8e5a8b.

I'd appreciate feedback on this and suggestions for other, perhaps better default colors for the document theme.

Maybe it makes sense to use Matplotlib's first color in their default cycler #1f77b4

tan (#D2B48C)	lightblue (#ADD8E6)	MPL's default #1f77b4

Personally, I think lightblue (#ADD8E6) looks the best all around. Not too light or washed out and not dark.

[codecov]

Codecov Report

Merging #4574 (b10e1e2) into main (518f322) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #4574   +/-   ##
=======================================
  Coverage   95.77%   95.77%           
=======================================
  Files         127      127           
  Lines       21357    21357           
=======================================
  Hits        20454    20454           
  Misses        903      903           

[akaszynski]

I also feel that lightblue looks the best, especially considering how these look with black edges.

[tkoyama010]

LGTM

[adeak]

Blue is always better 😁

[bjlittle]

FWIW I vote for light blue too 👍

[banesullivan]

Well alright! I didn't expect this to be embraced so enthusiastically and quickly... suppose I'm not the only one who was tired of tan