Designing solutions to help color blind players play the game more effectively definitely translates to UI design, and it should. Normally, devs make color-blind modes, and such – as seen in AoE2:DE and others. That’s part of UI design. I’m fully aware many studios do this, as I’ve previously noted. I’ve actually voiced concerns for UI/UX design and visual solutions with color-blindness in mind at random times quite a while at non-game industry jobs; when nobody else around me on my teams probably even thought of it, let alone brought it up in meetings. (I can attest that nobody ever brought it up but me; and they always seemed like it had never been a thought before).
Regardless, you’re taking my hypothesis I stated above (which I don’t really know if you actually read that particular post, or if you’re just going from my latest post with the photo) and twisting it to be as though I think that is definitely the case; which is completely incorrect. If I made it seem like I had 100% formed that conclusion, my apologies. I didn’t.
I said it “could be” that they wanted to level the playing field for all players by making the icons the way they have; and then I asked what people thought, so we could discuss. It was a hypothesis from left field, as I hadn’t thought of it before and haven’t read anyone theorizing it before. I never said I believe they probably did that. There’s a difference. To be honest, I believe they just wanted to make a slick UI fit for 2021, or much more consistent with modern day Microsoft standards for UIs. After my thought from left field, though, I think there’s a 0.05% chance the icons are as they are because they maybe wanted to level the UI/UX playing field for all players by making universal icons that look the same for all players regardless of color-blind or non-color-blind. (Nothing inherently wrong with that, and would seem noble, but it’s something we’re not used to for AoE, and I think there are probably better solutions that’d be more widely accepted and beneficial to all.) AoE4’s gold icons are completely color agnostic; using purely contrast and shapes/silhouette to communicate their intent. I can’t speak from personal experience, but I’d be curious to know if the default gold icons are completely readable for most or all forms of color-blindness due to the icons mainly just relying on contrast and silhoutte.
Additionally, ‘Accessibility’ applies to multiple facets of life, not just color-blindness… and it can lead to periphery discussions about different learning styles and different approaches to everyday things to cater to different subsets of society. So, I surmised that during the color-blindess presentation, they also maybe touched on those things.
All in all, it just seems a little odd to me to not have icons that the more visual people of the world can identify with. Making a lot (most?) players rely on muscle memory to navigate the UI seems like a very strange solution to me 
But I digress…