Illusion knitting is so intriguing, but I've never been able to understand the directions. And most of the patterns I've seen were for scarves, which aren't exactly my cup of tea. But then . . .
A helpful knitter/enabler pointed me toward an illusion sock pattern. Free, too – my favorite price. It's called Alice's Illusion Socks ("Wonderland Socks" on Ravelry) and it is cuter than cute. I couldn't resist.
How does the illusion work? Well, it's a lot easier to understand when knitting in the round, because you are always on the front of the fabric. Each row of the pattern is done four times – twice with gray (kitty color) and twice with white. Rows one and three are easy – just knit around, no worries about the pattern. On row two you KNIT around (with gray) and PURL the kitty stitches. On row four you PURL around (with white) and KNIT the kitty stitches. That's it. The gray purl bumps make the picture, while the white knit stitches create a little valley that provides the view of the picture.
The pattern as written is toe-up with a short row heel, but I changed it to cuff down with a flap-and-gusset heel. I managed to divide for the heel at a point that left enough room on the foot for the remainder of the pattern, but it was a close call. I was prepared to shorten kitty's tail a bit if necessary. And since the tail needs to go up the outside of the leg, it was important to mirror-image the pattern from one sock to another.