New Triangle Color Picker
Create a new picker like:
- https://affinity.help/designer/en-US.lproj/index.html?page=pages/Panels/clrPanel.html?title=Color%20panel
- http://product.corel.com/help/Painter/540230868/Main/EN/Win-Documentation/wwhelp/wwhimpl/common/html/wwhelp.htm#href=Corel-Painter-Using-temporal-colors.html&single=true
- https://coolorus.com/

As far as I can tell, there is no library providing support for a web version of this color picker.  

![image](https://user-images.githubusercontent.com/20903247/74495169-0c3b3a80-4ea5-11ea-90c3-c96284cb938d.png)
![image](https://user-images.githubusercontent.com/20903247/74495231-2ffe8080-4ea5-11ea-824b-ff34260c23f6.png)
![image](https://user-images.githubusercontent.com/20903247/74495241-3856bb80-4ea5-11ea-8bd0-c31925cb7760.png)

The closest thing I could find is a code sample available on codepen, which is automatically MIT licensed.  The interaction may need more finessing, as it’s not as smooth as Affinity’s version.
https://codepen.io/graphilla/pen/NpaXNm

Why?  I’ve spent weeks solely picking out colors by hand.  This color picker was the best.  I like it so much that I’m building a plugin with the codepen code just to have a triangle color picker back in my new software.  I think it’s a great fit for this library too.  Any chance this addition could be made on the 3.0 roadmap?