It works on a boy, but I prefer it on a girl. I think most people would assume a Sky to be a girl. I like Sky for both genders. I only like Skye on a girl. Sky is my favorite spelling most of the time, I usually think Skye looks slightly misspelled. I like SkyWilliam, SkyTheodore and SkyThomas.
Yeah, you are right. Most people would assume a Sky to be a girl. I think that's maybe why I went with traditional middle names. I admit I liked the androgyny of Sky juxtaposed with a more overtly masculine name.