Notes do not have timbre, they are just named pitches (which themselves are just frequencies).
So, in JI you wouldn't simply use 'A' to represent (e.g.) 440Hz, it might be A 4, for the "A" key (or "A" staff position) having a 4 cent difference than ET A.[1]
1. http://lilypondblog.org/wp-content/uploads/2015/11/example.p...