So what is business formal? Below are a few descriptions.
During the Induction Ceremony, males typically wear full suits in dark grey, black or navy. Sticking with dark colors is usually the best idea. Either two button suits or three button suits are fine. Lighter colored suits and four button suits tend to stick out from the crowd (in a not so good way).
The bottom of the pants should be touching your shoes (avoid highwaters).
Try not to wear brightly colored or flashy ties that stick out. The length of the tie should be so that the bottom tip of your tie should meet with the bottom edge of your belt buckle.
Try not to wear brightly colored or flashy vests that stick out. Vests are optional.
Dress shoes (black or brown are the most common that compliment suits)
Women can wear a two pieced matched suit in either the style of pant or skirt. Appropriate colors include grey, black, or navy. Skirts should come to at least knee length while standing. Stockings that match your skin tone or compliment the suit can be worn with skirts or pants. The blouse under the jacket should be of a conservative color and/or pattern.
Closed toed shoes are professional (avoid extreme shoes such as stilettos).
Keep the worn jewelry conservative (do not wear dangly earrings or large necklaces).
An example is shown below.