An article from FSM by a professional modeller, uses the dipping method. I think its kinda messy and wasteful for the paint.
The method calls for:
1. Paint the whole bomb.
2. Dip the bombs on the yellow paint upto the level required. Hang and let dry.
3. Dip it again using the green paint depending on the thickness of the yellow band.
4. Dip in silver paint for the fuse.
Hope u find these useful.