Am i missing something here? How about "it could be simply 'White Wine' sauce"? (onion, white wine, bit of sweetening [depending on what wine], butter, flour for thickening)
Please don't use margarine in a sauce, use butter, preferably unsalted. If you are worried about the calorie content then don't have the sauce.
Back to the question....there are literally hundreds of sauces that contain white wine and onions, hence the need to be more specific.
If it's mainly onions and it's a white then it could be a soubise sauce. A brown/clear sauce could be used in a Lyonnaise dish. White Wine sauce doesn't really reduce your options as white wine/vermouth is used in so many sauces.