On any other day in 1892, Plessy could have ridden in the car restricted to white passengers without notice. According to the parlance of the time, he was classified "7/8 white."(Thanks to our regular commenter Beth for emailing me that link.)
In order to pose a clear test to the state's 1890 separate-car law, the Citizens' Committee in advance notified the railroad — which had opposed the law because it required adding more cars to its trains.
On June 7, 1892, Plessy bought a first-class ticket for the commuter train that ran to Covington, sat down in the car for white riders only and the conductor asked whether he was a colored man.... The committee also hired a private detective with arrest powers to take Plessy off the train at Press and Royal streets, to ensure that he was charged with violating the state's separate-car law.
Everything the committee plotted went as planned — except for the final court decision, in 1896. By then the composition of the U.S. Supreme Court had gained a more segregationist tilt, and the committee knew it would likely lose. But it chose to press the cause anyway.... "It was a matter of honor for them, that they fight this to the very end."
February 12, 2009
"Keith Plessy and Phoebe Ferguson stand on the railroad tracks at the corner of Royal and Press Streets..."
"... where in June 7, 1892, Homer Plessy was arrested after boarding a train designated for whites only."