The han-eri is a removeable collar, just loosely stitched over the neckband of the juban kimono, so it can easily be removed for washing or changing. Sometimes special clips are used to hold it in place instead of stitching.
The edge of the han-eri is visible when the outerwear kimono is worn on top of the juban under-kimono. It is a feature of the kimono ensemble. Kimono wearers will change han-eri to get a new appearance or to co-ordinate with their kimono & obi ensemble.