Final answer:
The White Dresses group chat was changed to that name at the beginning of the dress code protest in Des Moines, Iowa in December 1965.
Step-by-step explanation:
In December 1965, a group of students in Des Moines, Iowa held a meeting to plan a protest against the Vietnam war. They decided to wear black armbands as a symbol of their support for a truce. The school administrators created a policy that stated any student wearing an armband would be asked to remove it. The students, Mary Beth Tinker and Christopher Eckhardt, wore their armbands to school and were sent home. The group chat that they used to plan the protest was changed to the name 'White Dresses'.