Advanced color settings wanted in Web Designer

I suggest adding support for color adjustments from within web designer. Not only the accent color, but the color of all the other theme elements within the app (as documented here). 
Currently, one has to adjust the colors manually in the app.json (within the branding item). As a start it should be possible to enter a different RGB or HEX value for each of the theme elements, but a color palette like the one used to set the accent color would be even better. 
 

It would also be great to have a reference that specifies what part of the app is actually affected by the different theme elements.