Colour-polarizing filters?

Was browsing through Horenstein's Colour Photography book and found this interesting passage about color-polarizing filters that produce varying intensities of a colour (or sometimes multiple colours) as you turn the filter.

Yet I haven't been able to find any information about these online much less any available to buy.

Anyone know about this?

The passage in question is attached.

Cokin made these and they show up on ebay from time to time
there are red and blue ones on at the moment

stay safe

robin