You're implying that if red's meaning in one situation is the same, then red's other meanings in other situations must be the same.
Okay I guess. I don't know why you would think that, but I don't have much hope of convincing you otherwise.
> all different and arbitrary
Those are the extremes of the spectrum.
Color choices are not at either extreme.
Most color choices are arbitrary, some of them are shallowly cultural, and some of them are deeply cultural.
HN having an orange banner at the top isn't significantly cultural. Traffic lights are worldwide culture. Black or green for positive money and red for negative money are US culture. Red for positive money and black or green for negative money are Chinese culture. These choices tie into older associations, which affects the depth. But even if they were shallow they'd still be culture.
Here's a link full of its own links https://graphicdesign.stackexchange.com/questions/6982/excep...
Or we can look at how old the western association with red as negative money is: https://grammarist.com/idiom/in-the-red-and-in-the-black/
If you wanted specific links you should have said so 4 days ago after I wrote "You can also do a text search for china red green stocks, or japan red green stocks."
If you want a citation for HN's orange not being deeply cultural, then you got me, I didn't actually check. But let's see... "The orange logo was chosen because it was the opposite of VC websites which were typically forest green or navy blue" yeah that's not deep culture.
Different choices have different levels of cultural depth. Often the depth is zero. But it varies.
And culture is created by arbitrary decisions coalescing into guidelines. If it's not coalescing, then it's not culture. You have to look at the big picture to tell if something is culture or not.