One of the worst features of South Eastern's main line stock is the high pitched hissing sound which seems to come from much of the lighting. In several years of travelling, on a daily basis, between the coast and London (typically 15 hours on board per week) I became concerned that it might be damaging my hearing.
Is this a peculiarity of the Electrostars or is it found more generally? Is anyone aware of whether this 'feature' could be eliminated and, if it could be, why it hasn't been?
Not familiar with that stock personally but you appear to be describing inverter whine, and I would say that being able to hear it is a sign that your hearing is better than normal!
I used to be able to tell whether or not the line output stage in a TV was working simply by listening for the 15.625kHz whine. I can't any more; nor can I detect inverter whine from caravan-type 12V fluorescent fittings these days, and my memories of hearing it in DC stock of various types are all pretty old too.
When transistorised inverters for fluorescent lighting first became practical they were more or less bound to whine, because the power transistors that were available and the laminated-core transformers that were common could not be operated with reasonable efficiency at high enough frequencies to be inaudible. With modern components this is no longer the case, and I would suspect that if it is still happening it is down to either continued use of ancient designs or laziness in designing new ones. Since most people can't hear it anyway, nobody is bothered...
Pale white does seem the way it's going though, especially with LED tubes in use.
It's entirely possible to make warm-white LEDs (and indeed I have an LED bulb made with them) - it's just a matter of using the right phosphor, same as it is with fluorescents. In both cases there is some loss of efficiency but it hardly matters. For some reason people won't use them though - warm-white fluorescents have been available for donkey's years, but people still prefer complaining about fluorescents being harsh and cold over installing different tubes...
The T12 fluorescent tubes in use before were better, but I believe these are obsolete now.
For certain values of "obsolete". They are still available, and sufficiently readily that they must still be being manufactured; it's just harder to find them. Which is silly, because they
are better - the larger surface area makes them less glary, they last longer, and they produce full output as soon as they are switched on even in cold weather, without needing to warm up (not so important for railway use, but for domestic use it certainly is).