What would happen if the segregation roles were reversed?
Q: What might happen if during segregation a ‘white’ person used facilities designated for ‘colored’ people?
A Historian’s Take: “Nearly every Jim Crow law provides for the establishment of separate facilities, structures, or areas for black and white people and many of them contain language that limits the movement of supplies across the race-line. Rosa Parks, as others in this thread have noted, was arrested and convicted for “refusing to obey orders of bus driver” Under the city code of Montgomery, bus drivers had “the powers of a police officer of the city… for the purpose of carrying out the provision of [segregation of the bus lines]” So, the simplest answer to your question — at least insofar as the bus system in Montgomery Alabama is concerned — is that the bus driver would be legally bound to order them to sit in the white section and the Courts would enforce that order as if it were a lawful order given by a police officer.
“Which is pretty much exactly how nothing at all worked in the South. The underlying purpose of the Jim Crow laws was to establish White Supremacy. After Reconstruction ended white-lead governments surged back into power and used their power to marginalize the black vote. They then used that power to enact Jim Crow laws which further suppressed black political activity and relegated black people to second-class status. While stated goals for this are hard to find and differ on a state-by-state basis, it’s illuminating to consider that white people were a racial minority in some southern states and a sparse majority in many others.”
Related: Black Americans Used to Have to Navigate Jim Crow Laws During Road Trips with this Travel Guide.