Washbasin faucet - cold and hot swapped!

A question for the experts
At our construction site, the plumber installed the concealed plumbing (after prior discussion about which fittings etc.) and we installed the fittings and sanitary items.

Now the problem is that for all wall-mounted washbasin fittings, cold water flows where hot water should be and vice versa.

He says that this is a construction error.
I just checked online with the dealer again, but the fittings only come like this.
Am I stupid now or is he trying to cover something up here?!

Happened to us too. Then I asked Grohe and learned by email that there is a replacement part that costs more than the shower faucet. Craftsman joke: You only replace the blue-red dots- I would call the manufacturer directly, they know more about it. Then you can tell the plumber if he is right or if he has to handle the case.

You might need a conversion like the Simpsons had in Australia so that the water flows properly

Ok, and who is basically to blame now? Us because we installed the "wrong" fittings or the plumber because he laid the pipes incorrectly?!

the plumber because he laid the pipes incorrectly?!

Did he really? What does the execution plan say about where the cold and hot water connections are supposed to be? Because that’s the only thing that counts.

Ok, and who is basically at fault now? Us because we installed the "wrong" fittings or the plumber because he laid the pipes incorrectly?!

Both can be wrong or right. It is exactly as says; this needs to be checked. In this context, there is no "wrong" fitting.