It’s pretty simple - they are the colors of Pittsburgh’s flag, which in turn, is based on the coat of arms of William Pitt, the 18th century British prime minister for whom the city is named.
While other cities have sports teams decked out in the colors of their flags - the New York Mets, for example - Pittsburgh is unique in that all three of its major teams go with the same color scheme.
It has not always been the case, as two of the teams have worn other colors in their histories.
The Steelers - originally known as the Pirates - have always had black and gold since their founding in 1933.
The baseball Pirates, who started in 1887, had combinations of red and blue before switching to black and gold in 1948. (Please try to forget about the terrible red alternate uniforms that crept into the Pirates’ color palette in the 2000s.)
Finally, the Penguins switched from blue and white to black and gold for good in 1980, despite the objections of the Boston Bruins, who somehow thought that two primary colors could be trademarked.
The Penguins went to the WABAC machine, however, to point out the city’s NHL history began with the black-and-gold clad Pittsburgh Pirates - yes, this is a third franchise with that name - in the 1920s.
The hockey Pirates wore “bright yellow wool jerseys with black trim stripes with a ‘P’ on the front of their jerseys in 1925-26. The team used the Pittsburgh’s city crest emblems from older police jackets on the uniform sleeves,” Pittsburghhockey.net has archived.
The ice Pirates only lasted from 1925 until 1930, one of a number of teams in the NHL’s early years that are not included when the league refers to its “Original Six.”
The ABA’s Pittsburgh Condors and Pipers didn’t get the color-scheme message in the 1960s and 70s, however. They went from blue and gold to red and gold before folding in after the 1971-72 season.