You were saying?...
You will note that I used the term 'competent', as in: no competent designer will voice a preamp or amp. The reason you hear those differences is often nothing to do with voicing, but rather distortion. Our ears hear distortion as tonality, which is why two preamps can measure absolutely flat on the bench, but one will sound bright (due to trace amounts of odd ordered harmonic distortion) and one will not (lacks the odd ordered harmonic distortion).
If the designer engages in 'voicing' they immediately introduce additional distortions or colorations that will limit the usability of the preamp! Instead they go for flat frequency response. ';Voicing' is poor engineering practice in amps and preamps (BTW with speakers this is a different matter).
So the key word here is 'competent'; any designer telling you they voice their preamp is also telling you they have no idea what they are doing. Sorry, just stating a simple fact. If a designer has to engage in such practice it is because there is an inherent flaw in their design- instead of a bandaid approach, they simply need to find the flaw and correct it.