Black players and Affiliated Minor League
 

Maybe it's a dumb question but as much as I search I can't find the answer... all I got is when the first black player played in the Major League.

So in what year they were alowed to play in the affiliated minor league system?

Jackie Robinson signed with Dodgers organization and played in Montreal (a minor league) in 1946. Brooklyn (majors) in 1947.
Officially Negro players were never officially "banned" from major leagues (or minor league) baseball. They just never found anyone good enough - their words not mine.. Anyway, wording aside, after Fleetwood Walker in 1884 (American Association Toledo - a major league level.) no one was given a contract to play in the MLB/minor league system until Jackie Robinson.

There was a smattering of black players - and even a couple of black teams - in the minors up to around 1898, although some of those minor leagues may not have been recognized as part of "organized baseball" by the established major and minor leagues. More information can be found here.