distinguishable matplotlib colours / symbols / line styles

[DL Neil]

On 17/12/19 5:19 am, Chris Angelico wrote:
> On Tue, Dec 17, 2019 at 3:16 AM duncan smith <duncan at invalid.invalid> wrote:
>>
>> Hello,
>>        Not really specific to Python or matplotlib (but that's what I'm
>> using). I'm looking for a good combination of colours and symbols for
>> scatter plots, and combination of colours and line styles for line
>> plots. Too often I find myself producing these when I don't know whether
>> they will end up being printed in colour or greyscale. It would be a lot
>> easier if I could produce decent plots that would work well in either
>> case. I can find various stuff on colour palettes, but pretty much
>> nothing on symbols or line styles. Is anybody aware of an approach that
>> works well? I'm aware of issues with colour blindness and RGB versus
>> CMYK. Ideally I'd have something that I could just use that would deal
>> with all these issues. TIA.
>>
> 
> I'd recommend looking at the Web Content Accessibility Guidelines
> published by the W3C; there are a number of tools out there that are
> designed to help you pick colours for a web page, and the same sorts
> of rules will apply here, I think.
> 
> Also, thank you for even *thinking* about this. A lot of people don't. :)

+1

We spend a lot of time teaching this topic (non-Python courses). It 
receives a lot of often highly-polarised comments/discussion. Many folk 
have their 'eyes opened' to an issue which has not affected them 
personally. Some even have to be informed that it is a legal obligation 
in their jurisdiction. However, it also receives the highest number of 
'why do I have to learn this stuff' complaints...

I learned (way back) that the incidence of "color blindness" is far 
higher than I had imagined. Secondly, that it affects males more than 
females. Thirdly, that calling it "blindness" is a bit of a misnomer, 
because whilst people often can't see red 'correctly' (most common 
symptom), they do see something (it varies). Which is why they are 
permitted to drive vehicles (traffic lights: red, amber/yellow, green - 
and arrows; plus stop/brake lights), but why many smart-phone apps/web 
pages which encode information-relevance (red is 'wrong' and green/blue 
is acceptable) can become almost unusable (without other cues).

Those key-words: "accessibility guidelines" will yield a swag of useful 
tools - ignore the ones which are basically 'help choose the color of my 
web page/color palette, because they are often aiming (only) for 
'pretty'. The best tools enumerate the efficacy of fg/bg 
color-combinations, allowing one to experiment; and will enumerate 
grey-scale variation/comparisons.


Hmmm, note to self (you've inspired me to specifically review/critique 
the printing-from-screen action): what happens when we take a 
color-checked screen display and print same but end-up viewing it as 
monochrome/grey-scale output? Probably not a main-stream demand, but 
worth tossing at the WCAG experts...
-- 
-- 
Regards =dn