That's not really what they meant by "acceptable" - just that either of those metals are traditional. What's "acceptable" depends on the people in the relation

That's not really what they meant by "acceptable" - just that either of those metals are traditional. What's "acceptable" depends on the people in the relationship, and what will make each of them happy. I didn't have a ring when I proposed to my partner as it was a fairly spontaneous decision when we were in a foreign country, and I knew the location of the proposal would matter much more to her than a ring. But then after we got back we worked together with a jeweller to design a ring, which made sense as she has better design judgment than me, and we weren't doing anything very lavish/expensive, just something tasteful that she would love (for the record it didn't have diamonds, but rather a morganite stone with white gold).