What’s the origin of pink=girl and blue=boy for baby stuff. I’m preparing to be a first-time grandma and was looking for some cool baby yarn. Pinks and blues with a smattering of ugly yellows and greens. Really?
There seems to be a debate over exactly when and how that happened; I note that the article for Pink on Wikipedia has a section on the matter.
Early 20th century, at least in US/Western culture (see cites). Before it may have been switched, but nothing is universal.
Or, what Knip Trihs said.
was-pink-originally-the-color-for-boys-and-blue-for-girls
Culturally speaking, things are changing. Pick whatever color you want. Babies look cute in just about anything. So what if people call my two month old a he when she isn’t in pink or flowers, she is still beautiful no matter what gender strangers think she is. 
Here she is wrapped in a gender neutral blanket. See how cute that is? 
As a suggestion, pick some completely different color like purple or red. Babies wear too many soft pastel colors IMHO and need to switch things up if they want to stay fashion forward.
This yarn is super soft and durable and comes in a variety of cool and interesting color combos.
A good discussion of this on QI wity Steven Fry.
In my experience, even when your daughter is dressed head to toe in pink and frills, some sweet old gentleman will stop you to tell you “He’s a fine little fella”, and be oblivious to your repeated use of the word “she” in your reply.
Lol. True 
Yoren?
How about holiday or seasonal colors? Team? National/ethnic?
Not fashion forward, but at least off the pink-and-blue beaten path. Check things like the Oriental Trading catalog for theme suggestions.
The first thing I’m looking for is the texture of the yarn. I want the soft, cuddly stuff that’s in abundance in pastel baby colors but nothing else.
Yes. I remember being in grammar school and reading some book from the library–it might have been about etiquette or something, probably from around the 40s-50s, and reading that pink was for boys and blue was for girls. I had just assumed that was a mistake until years later I found more references to pink=boy, blue=girl. The Straight Dope article seems to indicate the last reference to this color scheme was from 1939, so perhaps the book I was reading was older than I thought.
You can get yarn online in any color and texture and weight whatsoever. You can get baby yarn spun to order from a baby sheep named Sophonisba and hand-dyed to your specifications. Baby items are so small that it is even kind of affordable.
I would go with cheerful primary colors, if I wanted to avoid pastels.
I was taking my older son out for a walk one day when he was still too small to sit up. A neighbor woman told me I had a beautiful daughter. As it happened, he was in a blue pram, wearing a blue jacket, blue hat and mitten set, blue wool socks, and he was covered in a blue blanket. I said thank you, he’s a boy. She asked, “With those eyelashes?” I said, “You don’t tell by the eyelashes.”
Heck with it. Dress 'em in what you think looks nice, let random strangers sort it out for themselves.
Others have adressed the “pink used to be for boys” thing. That same info is the best of my knowledge.
Agreed you can choose any yarn you want. So-called “baby” yarns are just machine-washable DK weight yarns in boring colors. 
So-called “Sock” yarns work great for baby items, I especially like “tonal” yarns with their blend of light and bright colors (example picture of tonal yarns).
If you limit yourself to common big-box store brands (which I don’t recommend you do) Lion brand Homespun line has a huge number of colors and is fluffy and machine washable. It’s Bulky and textured though… its no good for fine, delicately made items. But then delicate work and “fluffy” don’t really go together. There’s a color called “Tudor” which is a cream yarn with a varigated blue-pink-green-purple part through it, that I often use for baby things. To be perfectly honest though, Homespun has its haters.