I like aquas in white metal, unless they''re super washed out, then yellow gold. I prefer cuprian tourmalines in yellow gold, but that''s because I think all of them have a slight green component, and the yellow brings that out (I like the green). If it''s a very light cuprian, the yellow gold gives it color. As for other light blue stones, it''s a toss up for me, and depends on the individual stone I guess.
For me, it depends on the shade of light blue. If there''s a grey presence in the blue, sometimes a WG setting will amplify that. I would just have to try the particular stone in different settings.
Sonoma, it depends on if the stone has any undertones that you want to play up or play down. I second the suggestion of placing the stone next to white and yellow metals to see which effect you prefer.