if it were almost anywhere else on the frame then yes maybe the paint ought not to have come off and yes touching it in would be a great thing to do. But where that wear/damage is , I think you might be wasting your time doing very much there at all; I think the paint will wear off that surface whatever you do to it.
If you take a look at a few well-used Bromptons you will soon see if any of them have their paint intact at this point. I suspect that none of them will be wear-free at this point, but this is something you can check easily for yourself.
The first blemish on anything new is always painful but when all is said and done it is a tool and it is there to be used, not set in aspic.
It may be worth trying one of the usual schemes to prevent creeping damage in high-wear areas, e.g. applying tape to the area. I don't think that will last either, in fact, but it may help rather than hinder.
BTW the paint will almost certainly have a RAL code 357 C, but not sure that actually helps. The Humbrol Brunswick Green I have looks like it should be quite a good match.
cheers
I've seen a number of well-used Bromptons that have just minor paint wear in this area after years of use, have not seen any that have had a whole strip of paint come off like this, though.
I have already applied hard-wearing clear helicopter tape to all the areas of the frame which are susceptible to rubbing by the cables or chain, I did that shortly after purchase, following a guide I found on the web. Those areas seem to be holding up well, but I wouldn't expect any wear after only about 100 miles of use anyway.
I don't know about a RAL code, but Brompton said their Racing Green has the Pantone Code 357 C, not sure that this actually helps in finding a better paint match, though.
Anyway, it's looking like I'm going to have to deal with this myself, as Brompton don't seem to want to help, and I don't like the idea of leaving that part of the frame as bare metal, so am back to looking for a suitable primer to use before applying the paint, still a bit unsure which zinc primer to get, as there seem to be lots of different types...