I know someone who loves amber and would love an amber engagement ring but not that one. Lighter, maybe even with an entrapped seed or insect.
I personally went with a non-traditional engagement ring. I'm also not a fan of diamonds or pink. But now husband was smart enough to suggest we shop together. So we went into jewelry stores and I showed him my taste, to give him some ideas. But he ended up buying my ring when we were together. And I wouldn't have ended up with it, if we hadn't, because it actually wasn't what I thought my style was. I tried it on because it was on a helluva sale.
So my advice would be: if you aren't absolutely sure what style the recipient likes, shop together. If the recipient picks out a bunch of different things and the giver picks one of them later, without the recipient present, great. If they buy it together, great. I don't think there is greater meaning to the ring just because the recipient didn't know what they were getting.
Heirloom pieces open up a whole 'nother can of worms, though. And I really think the recipient needs to be in on it, if there is anything unusual about it. I mean, if I was Kate and William surprised me with Diana's ring, I'd be like, 'Hell, no. I'm not wearing your dead mother's ring.' I'm thinking they must have discussed it ahead of time and Kate was OK with it. If he surprised her? She's an incredibly tolerant woman!