Simple Knits for Cherished Babies, though the pattern is single-colour and only my interpretation uses two colours. However, I really like the way they've turned out, and they've inspirired me to try to create my own pattern... different than this but perhaps similar in style.
The seaming on these has major problems - ironically enough, I figured out where I was going wrong on the last couple of stitches, on the last bootie. It figures. But at least I'm fairly confident that for the next time, I'll know how to seam it so it truly is a flat, invisible seam. (whereas right now, the seam is flat on the one side but not the other - so when the cuff rolls, as in the photo, it looks shocking)
The first bootie is clearly distinguishable from the second - I hadn't worked out the colouring "quite" right so down one side the stitches are the wrong way around. (it's easy to see on the bootie, but not visible in the pic - deliberately!) Also the first bootie has a very minor sizing error - that is, at one point I was working with less stitches than I should have been - but it's not greatly noticeable either in eyeballing it, or in size.
Also, strangely enough, it was the second bootie I had tons of problems with. I had to restart the bloody thing about five times, and even then I ended up "tinking" a few stitches. Therefore, while bootie #1 was knitted in under 2 hours - including stopping, reading techniques, and going v..e..r..y slow in order to figure out the pattern, bootie #2 took me at least 3 hours, counting all the false starts, and caused me to stop knitting entirely for a 24 hour period (tho it helped that I had other distractions as well).
And YES - they do fit Z! Technically these are supposed to be 3-6 month size, but considering Z is 2.5 months, it's close enough.