According to Wikipedia:
Literally "Red and White Song Battle," the program divides the most popular music artists of the year into competing teams of red and white. The "red" team made up of all female artists , while the "white" team is all male. The honor of performing on Kōhaku is strictly by invitation, so only the most successful J-Pop artists and enka singers can perform. In addition to the actual music performances, the costumes, hair-styles, makeup, dancing, and lighting are also important. Even today, a performance on Kōhaku is said to be a big highlight in a singer's career because of the show's large reach.
Finally, it was revealed today that DBSK will be attending!