Summarize this article:

Ask your date if she has any favorite colors and, with her input, choose a few colors you both like to base your outfits around. Aim for two or three colors at most. From here, you can find a corsage that fits both of your outfits. You might choose a color scheme based on the seasons. If the special occasion is near Halloween, you could choose orange and black. If you're going to a Valentine's Day dance, you could choose pink, red, and white. While you'll buy your date a corsage, she will usually buy your boutonniere or corsage in return. Ask her what she's planning to purchase so you can buy a similar flower. You might coordinate on the flower type, color, or special accent. To draw connections between you and your date's outfits, buy a corsage that matches a color featured on your outfit. That way, even if your boutonniere does not resemble her corsage exactly, your outfits will match. Rather than the primary color, focus on the color of your tie or similar accessory. Seeing her dress beforehand will help you coordinate your outfits and your flowers, as well as what type of corsage you buy. The two main choices are wrist or pinned corsages. If her dress has sleeves, choose a corsage that you can pin to her chest. For strapless or sleeveless dresses, a wrist corsage will work best. If you decide on a wrist corsage, measure her wrist to order the right size.

Summary:
Determine a color scheme with your date. Match with the boutonniere or corsage your date buys for you. Pick a color based on your tie, cummerbund, or vest. Look at a picture of her dress before you buy the corsage.