I love Thing 1 and Thing 2! When my son was younger, we dressed him up as Thing 3 for Halloween (our mini schnauzers were Things 1 and 2 -- they wore toddler t-shirts that we got at Universal Studios on a trip one year). Anyway....
For the blue hair, I went to Michael's craft store and got royal blue yarn. For my son, I cut it to lengths and sorta glued it to a disposable processing cap from Sally's. I used Tacky Glue (I think that's what it's called, it dried but remained sort of flexible). Was not perfect Thing hair, but was good enough!
My dogs had their blue hair too, but was much harder to keep it on them. They couldn't trick or treat with their blue wigs, as we originally planned. Not that you wanted to know that! LOL
Type: 3b/3c (i), below shoulder length. Modified CG since 5/2004; growing gray since 5/2007.
CO wash: A-O GPB LYY, Salon Care Honey Almond, Devacurl OC, rotating others
Leave-ins: BWC, KCKT, coconut oil overnight
Styling: BRHG, MGA Sculpting Gel, Aubrey Organics Mandarin Magic Gel, LOTD AVG, LALSG
DT: Terax Crema, Moroccan Oil Restorative Mask, Je Veux Revitalizing Mud Mask