there is a really good one on the first "hot-lead" DVD.
but also here in the articles:
http://www.coolminiornot.com/articles/1164-hawks58-senmm
http://www.coolminiornot.com/articles/1191-reflecting-on-senmm
but probably a google-search could turn up quite a lot of relevant hits too.
edit: but in reality it comes down to:
having a transition from blue to white (top-down, so yes, white is down) to about half of the are or below (depending on how much reflected sky you want)
then having a really dark brown to lighter brown transition (top-down again, so yes, the bottom of the area is the lighter brown.
aaaand that's it basically. How it should look on curved surfaces could be best learned by looking at similar shaped objects from real life.