Roses are red, violets are blue. I see colours, do you see them too?
Yes you obviously do; all of them if you’re not colour blind. But, is the blue I see the same as what you say? It is like referring to two different people with the name Sai. Are they the same? No.
Then how can I say that the blue you see is the SAME blue that I see.
This is one reason why (maybe) Physicists never use the names we have assigned to “colours”; they always speak in terms of frequencies or wavelengths since they are measurable. “Viridian Green” or “Turquoise” is immeasurable. Although I must say, the entire electromagnetic spectrum is named based on the names assigned; Ultra-”violet”, Infra-”red” but let’s cut them some slack. It would be pretty complicated to have those regions of the EMR named after the numerous wavelengths they span.
Anyway, this makes the theory that “Everything is a social construct” more like a fact. But I am neither a rebel nor a reformist. Hence, I shall leave someone else to speak about that.