Browsing through my photo collection, I found an official LT photo of RM121 which does not have the ticket box painted black; I'd say it's red. In the same collection, an official pic of RM1923 with illuminated ad panel has a black ticket box.

Any idea what numbers had red ticket boxes? when were they painted black?

My bus number (if any): RML2532 GS67 BEA MLL721 BEA MLL738 RT2629

I thought I knew this but just checked Ken Blackers book 'Routemaster' to refresh the grey matter.

The last three pre production RMLs, 901 - 903 were delivered with Black ticket boxes. These were also the first vehicles with GRP painted exterior panels.
RMs constructed during this period ranged from RM865 to RM 1084 so it's possible that RM1085 was the first.
But unless I've misses a paragraph somewhere there's no other detail.

But timewise it must have been between November 1961 and January 1962.

RM1064 onwards, or so its says in the Haynes Manual (page 92).

Sorry - I could not resist the advert.

My bus number (if any): RM1368

Ah! Will that be p.92 of the Enthusiasts manual or p.92 of the Workshop manual? ???