A long time coming -- wicked long. In fact, 12 years after Jackie Robinson broke the color barrier, in 1959 Elijah "Pumpsie" Green joined the Boston Red Sox. Here's an interview with Pumpsie reflecting on his experience: http://www.nesn.com/2009/07/pumpsie-green-content-with-his-red-sox-legacy.html?ccrm
I wonder whether Jed Lowrey knows the significance of the number he wears as the current Red Sox shortshop. In my mind, #12 for the Sox belongs to a shortstop from 50 years ago -- Pumpsie Green.