Filters for Zeiss Super Ikonta

I have a Zeiss Super Ikonta 6x9 folder with the Tessar 3.8 lens. Does anyone know what filter type or size would be compatible with this camera. I shoot black and white with it and am interested in a yellow or orange and maybe a green filter. I don't see any threads on the lens, so I assume it would use some type of slip on filter. The camera is an early 1950's vintage. Any help would be appreciated.
Tim

At least some Zeisses had their own filters with a bayonet-type mounting (push and twist). I have an Ercona with its own yellow filter.

Get a millimeter ruler and measure the lens for a Bay adapter that pushes on. My Super Ikonta was a 6x6 and I used a bay 6 adapter that I also used on my Optar and Ektar 4x5 lenses. Depending on the adapter you get the same size filters. There wasn't a lot of meat to the front of my Ikonta lens (Jena) that the adapter could hold onto, but it did.

37mm dia and they do slip over the front. $15.00 plus or minus. Call Jims camrea in seattle. That is where I got mine. He also has 1.5 and .7 proxars. I think he has a couple of yellows and a red that I passed on as it had a cracked ring.