The instructions written for it in my newsletter were:
"This doily is worked in 2 complimentary colours of size 20 Opera
thread, one Light and one Dark, and is approximately 10 inches square.
The stitch count is 8-8 for both the rings and the chains. You’ll notice
that it shows 4 shuttles being used for this design and that is because
you need to use either 2 spare shuttles wound in the colours used or
you need to use two double bobbin shuttles each wound with both
colours in order to tat the many split rings in the right colours."
Here's a picture of the doily in question. It's a simple continuous design once the centre block is done.
The instructions state that when tatting the split ring using a double bobbin shuttle you can just use the Dark colour on the second shuttle. If you are using 2 spare shuttles you will have to hide the end of the spare Dark thread in the first half of the ring and then tat over the bottom of the ring thread and the Light colour shuttle thread with the spare Dark thread.
Since I don't own 2 double bobbin shuttles, I obviously didn't do that when creating this doily. By using my method of adding thread and hiding ends shown in my side bar you add and remove the alternate colours as you work. It's fussy, but I think not as fussy as having to deal with double bobbin shuttles that don't let the individual bobbins wind freely.
I've just finished the split ring part of the bookmark in one colour and now I'll go grab a couple of extra shuttles and see what it looks like done with 2 colours.