Chris,
Personally, I like your "sky"... but if you go outside and look on a nice, sunny day, you'll note that if you look up at a 45° angle, then slowly lower your view until you see the horizon, the sky becomes lighter and takes on a slightly green-ish tone. (I'm not a scientist, but I believe it has something to do with the effects of the atmosphere -- as you're looking towards the horizon, you're looking through "more" air, and the light becomes more diffused...)
Many of the articles I've seen in magazines start with a "darker" blue at the top of the backdrop, a "lighter" blue with a wee bit of green at the bottom, and then blend the colors together in the middle. I recall seeing one guy use four different shades of blue (darker, not so dark, lighter, lightest) to try to get that blended look.
Hope this helps!!
Regards,
Tom