Thanks @rokejulianlockhart , may I ask, are you visually impaired? I think one of the key areas people miss with a11y is that it’s not black and white (pun intended) 
For those of us who are in that middle ground where we have low vision (not blind, but not fully able to see either), is that monochrome symbolic icons can actually make things cognitively worse at small sizes, - such as launcher menus and system trays.
I can still differentiate using colour, texture and depth, flat and grey is just a blurry mess at small sizes. Anecdotally, I’ve had reports from people with normal vision that they use colour and texture to differentiate too. With the hard-coded symbolic icons, I have to actively try and read what that icon is, rather than going, “oh, that’s a blue icon, it’s x!” - cognitively, that recognition of colour takes milliseconds. Having to scan and work out what icon is what, based on the text that relates to them, takes seconds, many seconds. It all adds up.
Appreciate the incredible work that @ngraham and the VDG group do. All I’d ask, is that a11y be something we look at as more than just a binary situation. People have varying degrees of vision, and low vision, and often that variance is temperamental. Thankfully I can work around this by using other icon themes for now, and the application menu, rather than the launcher. But hardcoding icons with no ability to switch, does affect your users. Sometimes that’s a net negative.