Here are some good ideas for September colors for your wedding. I love this one color that is a light green. I understand that this is not a fall color. The light green would go beautifully with a darker green or a darker red/orange. This would "ground" the color in a more summer-fall transitional theme. You could use three colors- the light green, a darker green (dark sage, hunter, etc), and pair it with a gold, yellow, burnt orange, or dark red for accents.
This would be a monochromatic color scheme with complementary accents. If you want to browse some more color schemes, go to any website and look up any color you would think would go nice with your wedding dress.
I am also trying to decide what colors would look nice for an October wedding. I am also interested in such colors like, wine/cream, wine/champagne, and wine/gold. I think those color choices compliment each other beautifully, particularly the wine, gold, and champagne. Other colors to throw in there that would go nicely would be a deeper shade of copper and another lighter/darker red. Because it will be in the fall time of year, we could always coordinate oranges in there as well with flowers and centerpieces.
I have an outfit that I would like to wear but I want to make sure that it is appropriate. I have winter white pants with gold & silver pinstripes and a long off white blouse. As a rule, you don't want to wear white because that's what the bride wears. However, since your slacks have pinstripes and the blouse is off white, if you could accessorize it, such as a gold scarf that brings out more of the "off white" color, then you should be okay. I really do think that that outfit would look really nice. Make sure that you bring with you some kind of a jacket or coat that why when you get cool you will have something to put on. On the other hand it would still bring the outfit out more if you were to wear something that it light and airy and that you can just hang on something on tie it to your waist.
Plum & silver sounds lovely! Silver accents would be lovely on your plum dresses. If you go for another color, it can over-complicate the look. As silver is the 'accessory' color (this means it's the color used to complement your main color, which is used in hints) then it would be very suitable.
But try not to put too much of the silver all over the dress. Having too much silver on the dress will not show the plum as much. Having like a shahs or a ribbon on the dress that is silver will be just as nice and you will be able to show more or the plum color and some of the silver color with out having to over power one of the other colors.
You could even have your bridesmaids put in ribbons or small flowers in there hair to bring out the colors of the dress.