I went over this in my Precious stones article:
http://www.coolminiornot.com/go.php?go=articlephp&aid=200&page=2&orderby=&levels=
it\'s towards the bottom of the page. Basically, you make white edges (or if it\'s colored, a white+color mix) and paint the inside blue, if it\'s totally clear, or colored with the objects being shown slighty lighter than in real life. Angela also has a good example on that page, too.