As I understand it, the great bulk of music from the Baroque, Classical, and Romantic eras are at least these days performed on equal temperament instruments. And yet there is still a great deal of discussion of the inherent colour of various keys used for compositions (not merely of the keys in relation to each other within a piece, which I can understand).
While many instruments (and indeed singers) clearly have a natural range and tone changes considerably outside of it, and while very large absolute pitch differences are clearly detectable even by the most tin-eared whereas others are cursed with absolute pitch, as a non-musician of a mathematical bent, I find it hard to understand, from a mechanistic perspective, how different keys in the same scale can continue to be coherently and consistently said to have distinctive colour with pieces composed for, and played with, equal temperament.
I'm somewhat confounded by composers, wishing to use all the forces at their disposal, of course choosing the key they think best supports their piece, such that, for example, a piece of child-like innocence might be composed in C-major as a result of the belief in the inherent colour of keys, such that there are very few examples to suggest that the key have any other character.
Is there some mechanism which I haven't anticipated or, in this context, is it just hokum? I apologise if, in my naivety, I have stepped into controversial territory.
UPDATE: I might clarify my difficulty. If most people only sense relative pitch (and certainly much music theory is based around that idea) and if a key is shifted in equal temperament then all those relative pitches stay the same. So I'm told one thing by these ideas, and then another by the idea that keys -- even keys very close together in absolute pitch of the tonic -- have colour. I understand that there's more to real music than oscillators (such as sympathetic vibration, string tuning, timbre differences etc) and would like to understand if and how this adds up to key differences. I certainly have favourite keys and want to understand what that means.