Make scatter plots gallery example colourblind friendly

[weiji14]

Description of the problem

The orange and green colours at the "Scatter plots with a legend" gallery example can be hard to distinguish for people with red/green colour vision deficiencies. We should choose different colours instead if possible.

v0.3.0 original colour	Deuteranopia (no green) simulation

The line that needs to change is this:

pygmt/examples/gallery/plot/scatter.py

Line 24 in 65b099a

for color in ["blue", "orange", "green"]:

References:

• https://developer.mozilla.org/en-US/docs/Tools/Accessibility_inspector/Simulation
• https://docs.generic-mapping-tools.org/6.1/gmtcolors.html#list-of-colors
• https://colorbrewer2.org/#type=qualitative&scheme=Set2&n=3

[ria-19]

Can I work on this issue?

[weiji14]

Hi @ria-19, this issue is already being worked on already at #1013. But you can find a list of other issues at https://github.com/GenericMappingTools/pygmt/contribute that we need help with. I recommend #908 which is not taken yet, though you're welcome to try another one too.

[ria-19]

Okay, Thank you!

[nathandloria]

Hello! Recently my group @munzekm @cklima616 @noorbuchi and I took up work on #1070. We did this work for a class and another cycle has recently begun in that same class. We noticed that there was previously work being done on this issue, however progress seems to have slowed. Our team would love to take up work on this issue if possible. We really enjoyed this project and would love to continue contributing to pygmt!

[seisman]

@nathandloria Thanks for your interest in this issue. I just pinged the original author of PR #1013. I'd like to give another one week to see if the author wants to keep working on that PR before you create a new one.