The swirl Ericofon is the product of changing colors in the factory. After stopping one color and starting the next, there's still some of the first color in the machine. The first few shells to come out are a swirl of the two colors together. These were normally considered garbage and were thrown away making them extremely rare. Some survived by employees taking them home. The example I have is from a color change going between gray and white.
Ron Thomas in England has a red/white swirl that's rather dramatic. I've also seen a couple of burgundy/white in Sweden, but these lack ear pieces and interior machining. I have not seen any others than these.