I finally decided not to make the contrast colour tie, after trying 2 different colours and giving up about 10 inches into the 80-inch (!) tie.
I decided to fasten the side with mini shell buttons instead. Here's a closeup...
And this is what it looks like on the inside.
So, details about this project...
Material: 11 balls of Debbie Bliss Baby Cashmerino in 207 (and I needed every bit of that - I had to undo the gauge swatch to have enough yarn for the button loops)
Pattern: Arisaig from Knitty Fall 05 in the small size
1. Used 3.0mm needles throughout - i.e. did not use smaller needles for ribbing
2. Lengthened 2x2 rib section significantly - I think it's about 3 inches
3. Ditched the tie around the collar - I picked up a large number of stitches and knitted a few rows of garter instead
4. Fasten with button by crocheting a button loop on the side of the right front
So there you have it.