There was a fair bit of discussion about colormaps - terrible, useful, beautiful - at IEEE Vis last October.   The viridis colormap was a featured one.   So was the traditional rainbow, which lots of info-vis and perceptual people piled on to criticize.

Among design criteria for a continuous-valued colormap is whether it's "sequential" (like the typical yt colormap, or viridis) or "diverging".   You'd want a diverging colormap to show signed deviations from a norm - where the eye should be caught by places where a value is either much less than, or much more than, something in the middle.   Is it worth offering a typical divergent colormap, as well as a new typical sequential one, in yt?

Note that among the Stefan van der Walt & Nathaniel Smith writeup ( http://bids.github.io/colormap/ ) on their development of better cmaps, they use Nathan Goldbaum's galaxy evolution as a test case for six (sequential) examples! => http://vorpus.org/~njs/goldbaum-galaxies-all-colormaps.mkv

A neat web site with sample colormaps - aimed at mapping discrete values on geographic maps, so not directly applicable but cool - is this, by Cynthia Brewer and Mark Harrower at PSU:
    http://colorbrewer2.org/
It has a library of predesigned cmaps, and lets you sift them by being colorblind-safe, photocopy safe, etc.

From: yt-dev [yt-dev-bounces@lists.spacepope.org] on behalf of B.W. Keller [kellerbw@mcmaster.ca]
Sent: Wednesday, January 06, 2016 12:13
To: yt-dev@lists.spacepope.org
Subject: Re: [yt-dev] Default colormap

There is a really excellent paper on designing color maps called "Color Sequences for Univariate Maps: Theory, Experiments, and Principles" that you can get here: http://ccom.unh.edu/sites/default/files/publications/Ware_1988_CGA_Color_sequences_univariate_maps.pdf

If we design a new colormap, this would be a good reference along with those scipy resources.  I personally would love to have an accessible, yt-custom colormap.

On Wed, Jan 6, 2016 at 11:50 AM, Erik Schnetter <schnetter@gmail.com> wrote:
I think there are several colourmaps that were created when Viridis
was invented. I personally like Inferno.

-erik

On Wed, Jan 6, 2016 at 11:34 AM, Nathan Goldbaum <nathan12343@gmail.com> wrote:
> I would also be for coming up with our own colormap. That said, I think
> simply modifying algae won't be enough, since it is too perceptually
> nonlinear.
>
> On Wed, Jan 6, 2016 at 10:32 AM, John ZuHone <jzuhone@gmail.com> wrote:
>>
>> I would go for modifying algae.
>>
>> > On Jan 6, 2016, at 11:30 AM, Matthew Turk <matthewturk@gmail.com> wrote:
>> >
>> > Hi folks,
>> >
>> > For a long time we've used "algae," which was designed by Britton
>> > about eight years ago, as the default colormap.  This has been really
>> > nice for "branding" yt -- if you see an algae plot, it's probably (not
>> > definitely) made with yt.  But it's also not accessible from a
>> > colorblindness perspective.  Stefan van der Walt has been giving some
>> > really great talks lately about building a better colormap for
>> > matplotlib (e.g., https://www.youtube.com/watch?v=xAoljeRJ3lU ) which
>> > culminated in viridis, which is shipping in recent versions of
>> > matplotlib and will become the default.
>> >
>> > In support of this, he built a tool called viscm which can generate
>> > reduced versions of colormaps to show what they would be like with
>> > varying degrees of insensitivity to color.  I've generated outputs
>> > from viscm of three of the custom colormaps we ship with yt:
>> >
>> > Algae: https://images.hub.yt/u/fido/m/d275d5e1-png/
>> > Cubehelix: https://images.hub.yt/u/fido/m/8e698928-png/ (I believe
>> > this is now also shipped with MPL)
>> > Kamae: https://images.hub.yt/u/fido/m/e0e40efa-png/
>> >
>> > I love algae, but it's not the best from an accessibility perspective.
>> >
>> > I'd like to propose that we use a new default colormap.  If we do
>> > this, I see two options:
>> >
>> > * Retain a "branding" by developing a new one either by using the
>> > techniques used by matplotlib (or one of the maps they opted not to
>> > use) or by modifying algae to be more accessible; looking at the
>> > response functions, I suspect it would be reasonably possible to
>> > modify it.  (Modifying algae is my preference.)
>> > * Use viridis (which we may then have to ship if we have older
>> > versions of matplotlib to support)
>> >
>> > -Matt
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--
Erik Schnetter <schnetter@gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/
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