Which color of gown will look good on me?
If you are fair then I think you should go for a stark colored gown. Maybe a hot red or fuschia pink. Try a new color like neon orange. Other colors that you can try are royal blue or emerald green. If it is a daytime event, try a lavender shade or a light shade of purple.
pastel colors would also be a good choice.
Your best bet is to pick among colors of clothing that compliment your skin, hair and eye color. You can get a free color analysis done at a website such as ColorChromatic | Be Chromatic
That said, if you are planning to wear bright makeup, you may be able to choose among brighter colors. If you tell me the name of a celebrity who has similar color hair and skin to you in the comments, then I can make you a picture with some colors that will be similar to your best colors.