I have always thought of the name as a girl's name because one of the characters of "Rainbow Brite" was a girl named Indigo. I also think of the "Indigo Girls". I haven't heard of it as a boy's name until I came to this forum. I don't think it is that bad for a boy, but I still see it as slightly more feminine than masculine.
https://www.behindthename.com/name/indigo/top/united-states
Also, some proof that this name can still be Unisex.
https://www.names.org/n/indigo/about
https://www.nancy.cc/baby-name/indigo/