Is there an 81B filter in 27mm thread?

So I have this lovely little folding Contessa, which takes 27mm filters. (It wears them reversed, so that the lens has the male thread, but I think they're standard 27mm threaded.) I was lucky enough to land a filter set (yellow/green/orange/red) in an adorable little Zeiss Ikon-branded case, but I'd really like to have an 81B or similar warming filter.

The original Ikolor filters are cheap and available, and were regularly made in 27mm, but I'm not sure which one I need, if any. Some sites claim the Ikolor C is an 81B, but I'm suspicious; most photos of it look more pinkish, like a "skylight" filter. I haven't been able to find a good list of what the various Ikolor filters actually are.

The other 27mm options seem mostly to be modern filters aimed at d*g*t*l users, for whom filters are not the usual way to adjust color temperature. If I wanted a UV filter I'd be set.

Adapters don't seem to be a very good solution, because of the reverse threading; I'd need to find a step-*down* ring to 27mm, and it would have to have an unusual form factor to fit physically on the lens. (There's a narrow space that the female threads have to fit into, between the male thread on the lens and the focusing ring---if you have a folding Contessa or Contina you know what I mean.)

Does the filter I'm looking for exist? Is there an Ikolor decoder ring? Are there other clever solutions I haven't thought of yet?

Thanks

-NT

Colour-correction filters (other than 1A) are no longer listed by Heliopan, though may still be stocked. Inquire at them.

Alternatively cut a larger (used?) filter and set it into a 27mm filter-ring of another new/used filter.
(Cutting to the needed precision may be tricky in DIY...)