The thread you're referring to was hidden. It was unfortunately largely comprised of people's opinions on what the icons should be, either in color or shape.
The project has in the past provided explanations as to why the icons are the way they are (the stock AOSP apps had their icons replaced so that they and the apps made by GrapheneOS have a unified appeance).
The thread was not really productive, and there's nothing really to act on when all it is is people telling us they don't like the icon. There are no plans to change them, and there is no alternative which would satisfy everyone. If we made the icons purple, someone would want them to be blue, if we made them blue, someone would want them to be pink, if we made them pink... and so on.
I'm personally not a fan of the insinuation that we would hide a thread which has actual productive discussion happening in it, but people will have their opinion regardless. There's not much else to say on the topic of the icons that hasn't been said already, and I am personally fully okay with the fact that not everyone is going to be happy with the icons, because I know that no matter what the icons became, someone would remain unhappy.