First Negro player I recall was Grant Fuhr --- Goalie for the Edmonton Oilers, think he made the Hall of Fame.. A couple others were notorious Enforcers / Goons Donald Brashear, Georges LaRaque & Peter Worrell.... I'd met Worrell on a couple occasions when he played here in Florida for the Panthers., good guy. But, yes there's never been a significant number of Negro players in the NHL...
Lots of theories as to why, but the one you'd hear most is economics... It's an expensive sport to play.. Skates, equipment, League & Rink Fees, Lessons etc...