On Wed, 19 May 2010 08:50:54 -0700 (PDT), "Dr. Sunil"
wrote:

I have a copy of the 1985(?) "Motive Power Recognition: London
Transport and PTE railways", and there do seem to be a number of
yellow painted service vehicles (at least they look yellow despite
being black and white photos!). Some do seem to be darker (maroon?)
however, maybe they were the older ones?

Not necessarily, any complete repaints would have been yellow anyway
with the chance of the oldest vehicles being most in need of one. Some
of the vehicles in older colour schemes were likely to be the most
recent in service before the colour change. The only sure method is to
identify the individual vehicles and verify their build date while
remembering that LT re-used railway vehicle numbers and in some cases
(EMU carriages) exchanged them.