Obviously being rejected by literary agents is a dark time and therefore it is appropriate to wear all black. You want to give the impression of an author in mourning.
During this difficult time it is wise to wear boots to give you extra support, dark sunglasses to hide your running mascara, a practical messenger bag to carry your rejected (but obviously brilliant) manuscript around in so you can pull it out dramatically wherever you are and look important (people with big manuscripts always look important) and a long flowy dress to remind people that you are a delicate creative being (this will make people who dis your writing feel guilty) and obviously you need a jacket to prevent your getting consumption.