Thanks, ladies. The sock yarn is cute, but I agree with the PP - if I had to knit longies in fingering weight yarn, I wouldn't put it on her ass, I would BRONZE them.
Alternating the yarns isn't a bad idea, Ingrid. It's the sewing in the ends part that freaks me out a little. If it's for a gorgeous Fair Isle, fine. But for longies ..... ? I dunno. I know, I know, I'm just lazy. I've got to get cracking on some wool shorts for her soon as well.
Those longies are so wonderful and cuddly, too. I've loved them.