> I wish to set the face of the Echo Area.

Not sure what you mean by that.

> However, how can I change the face only a buffer with a given name using
> face-remapping-alist ?

(with-current-buffer (get-buffer " *Echo Area 0*")
(setq-local face-remapping-alist ...))

Great idea. Thank you.

I did not notice that Echo Area is a permanent buffer, despite that it appears all the time via (buffer-list).

I thought that it is killed all the time and re-created after /before each print0 call...

I was going just now to insert some code in the start hook of *fundamental-mode*, that checks the name of the new buffer, see if it is "Echo Area ", etc.

:) I was on a wrong way . Thanks for the quick answer.