I’ve never had any special value attached to ink colors. I’m male, in my early 30s, and grew up in California if that helps. Even in school, we could use blue or black as we saw fit and the only gender difference I noted was that the girls would generally write notes to each other in pink or purple. Many teachers had decided that green was preferable for correcting papers (rather than red).
Personally, I prefer blue. In large part, that’s due something someone mentioned earlier - that it helps you identify an original document from a fax or photocopy. In an age when anyone could copy anything in black and white, blue seemed a more personal touch.
On the other hand, I haven’t hand written a letter since I got out of school and didn’t do it much then.