I understand your problem @mozit, for the icons are Yaru, but of a different colour. It is absolutely related, for 1) got the original Yaru themes working for Unity #2017, 2) got a way to change the icon colours, #2025 - Yaru-grey.
It took quite a long time to read the whole thread. The majority of posts are just nothing. @mozit promised to do something on the way, btw, but I can’t find the result.
When, I read the question of @initu-icr #2009, thought maybe I’d look for it, not just promise, but do it. Test the result at least 12hrs, and if it works, show it. And, most probably, not for you.
Maybe, the Mate guys might want the green icons,