I do not like any of the women in question or think romantically about them.

Okay, but I'm going pretend you do, because I don't think you'd have a problem complimenting them if this were the case.

It's always safe to compliment hair, and assuming you're being sincere (that is, their hair isn't a complete disaster clearly unworthy of a compliment at the time) they'll like it.

You just need to talk to them like they're people, not an object of your desire. If it's going to happen, it will happen quickly and as long as you're paying attention to them, instead of your own insecurities, you'll see it. The biggest mistake people make is missing the clues in either direction--that they are interested or they aren't. You haven't "wasted time" if they aren't interested, because as long as you don't take it personally and get hurt about it, you just expanded your network by one.

You can't make it happen, it happens or it doesn't. Don't be discouraged. You can avoid being discouraged by not obsessing over them for days or weeks before you try them. Ideally, you make an attempt within a day or two of meeting them, they already know, just like you already know. That way, if it doesn't work, you don't feel like you lost something. There's no penalty for trying too soon, but waiting is a mistake.