[Dion]

In the 1940s, some teams had begun voluntarily to wear contrasting colours (including Montreal’s now odd-looking original white uniform), but at the NHL meetings in 1950 the use of contrasting uniforms became mandatory. The reason was due to the increasing number of motion picture newsreels being made of the action (which would soon become black and white television), that the NHL required each team should wear contrasting colours to make it easier for viewers to distinguish the teams during the black and white broadcasts.'

The home team would wear dark, the visitor white. It was Hockey Night In Canada that suggested that the NHL switch in 1970 to the home team wearing white jerseys in order to show off visiting team’s away jerseys (which were deemed more interesting) for colour broadcasts. Which team wears the dark jerseys has changed back and forth in the forty years since, with currently the home team now wearing the dark.

https://thehockeywriters.com/a-brief...-nhl-uniforms/