Regarding the history of yellow ends, I understand steam locomotives were more visible because of the constant plume of smoke. In most other countries, the solution to the invisibility of modern trains from the start was bright headlights. In Britain, however, bright headlights were not allowed because of the fear that they could render the weak gaslit signals invisible to the driver. The solution was compulsory yellow warning panels, which remained after headlights were added.
Back on topic, I was surprised to read in another thread that TPE had an option on more EMUs, but not more carriages. I would've thought, given the uncertainty of electrification, that it would make more sense to order more hauled carriages. These could then be hauled by locomotives of both types, depending on the level of electrification (though the Class 88 would only be powerful enough for such services in electric mode). After all, we already have high-speed push-pull carriages on the ECML, and also in some other European countries. The only future proofing required on the carriages would be to get them approved for 125 mph operation, which I believe they will be.
That said, it now seems The surplus Class 185s, which still haven't found a home, could make up for the shortage of non-electric new stock.