I’ve had some time to think about this, and a question has arisen: what, technically, is tone colour? I thought there was nothing to sound but frequency and amplitude.
Most analog means of sound production don’t create a perfect sine wave tone; they actually produce a large number of superimposed waves, with imperfections in the reproductions depending on the means of production. Tone colour, or timbre, is the combination of all of these ‘imperfections’. The Wikipedia article on timbre has a reasonable summary.