DOC/projections: Consistent design of examples

[yvonnefroehlich]

While working on PR #3451 I was wondering whether we should use a consistent design for all projection examples, especially the identical colors for land and water masses. I feel generating all examples in the same design looks better and more professional.

Current version	Suggested update 01 (one design for all examples)	Suggested update 02 (one design per category)

[seisman]

In the GMT 4 cookbook (https://www.soest.hawaii.edu/gmt/gmt/html/GMT_Docs.html#x1-990006), most projection examples are in white and black/gray. I guess Paul and others updated these examples to make them more eye-catching and also demonstrate how to specify colors by different ways in GMT.

I prefer to keep these examples unchanged, but let's hear from other people's thoughts.

[yvonnefroehlich]

Interesting (I started with GMT 5.x). Maybe having one color per category is a compromise here?

[seisman]

Maybe having one color per category is a compromise here?

Not bad.

[yvonnefroehlich]

Ping at the other @GenericMappingTools/pygmt-maintainers for their thoughts🙂.

[weiji14]

Yep, I'm ok with one color per category too (but not that yellow-ish palette please).