Yay! It's finished, only took 2 1/2 months (primarily knitted on bus journeys and a road trip to Paris and back). It's about 36in X 28in
Yarn: I used Bonus DK in purple, blue, green, yellow, orange and red.
Using circular needle - size 3.25mm.
Cast on 208 in Purple.
1 (WS) and all other odd rows: p
2: k1, *LT, k4, RT; rep from *, end k1
4: k2, *LT, k2, RT, k2; rep from *
6: k3, *LT, RT, k4; rep from *, end last rep k3
8: k4, *RT, k6; rep from *, end last rep k4
10: k3, *RT, LT, k4; rep from *, end last rep k3
12: k2, *RT, k2, LT, k2; rep from *
14: k1, *RT, k4, LT; rep from *, end k1
16: k8, *LT, k6; rep from *, end k2
17-32 : Repeat rows 1-16
33 and odds to 63: P
34 and evens to 64: K
Repeat rows 1-64 in each colour. Cast off, sew in yarn ends.
LT = Left Twist, RT = Right Twist
(I got the stitch pattern from Knitting on the Net, and this is how I turned it into a blanket).