Accessibility: Provide high contrast interface option

[alisterscott]

Originally raised by @supernovia

Provide a high contrast interface option for users with reduced visibility, as per forum discussions.

[SiobhyB]

Also raised in p4vt7e-27-p2.

Some users have great difficulty navigating with the default colour scheme. It would be nice to offer a high contrast alternative.

[folletto]

Noting that this to happen needs:

1. The architecture for the colors to be swapped dynamically
2. A color scheme (or more, ref the more general discussion on A11y) built on that architecture
3. The UI to switch color scheme.

The first step is happening in #15731. :)

[designsimply]

Noting that we are discussing increasing icon and text contrast in the sidebar (internal ref: p58i-6Ts-p2).

[kristarella]

+1 in ticket 1470890-zen

[cecoates]

Chiming in here to say that now we're "Calypso-fying" more stuff, such as WP-Admin pages, I struggle to use Calypso often because of how little contrast and color variance there is (I'd be described as having "protonopia").

As we make more and more Calypso-fied, it would be nice to have this option revisited.

In my case, icon and text contrast really isn't enough, when it can be hard to distinguish entire sections of the site from one another.

I have a similar issue with how paragraph blocks in Gutenberg have zero border around them, leading to clicking randomly to find out where the input area is.

[Aurorum]

I think this is fixed now with the new colour schemes added to Calypso?

[jsnajdr]

The new color schemes all have higher contrast than the original scheme and all pass the WCAG AA requirements. See also: https://en.blog.wordpress.com/2019/01/08/customize-your-wordpress-com-dashboard/