That was very good of you to photo that for me. I see what you mean the yellow just looks like a sleeve.
I am going to investigate this weekend by taking the easy wing off and having a look to see what I can do and take some measurements If I do manage to find a H4 modification I will obviously have to decide on yellow or white light   decisions decisions

The yellow on most lamps available now is indeed a sleeve. That makes life sooo much easier, as you can re-use the sleeve up to a certain extent, which means that you need to buy only one set of yellows - after that, white ones’ll do the job!!

Derk

I had one on my 2cv Fourgonette so I took it apart (easily) and found also it is plexiglas not glass so as you say could outlast a few bulbs
Taking the wing off tomorrow so maybe a photo to follow.

There are however white lamps that are not long enough! The yellow glass sleeve fits but on some DS types the connector gets flipping off the connector pins! I do not know specific brands but compare when buying!

The connector is the big one that has to be screwed on to hold the lamp.