Similar research was done using English soccer leagues, where the lighter the colours trended more frees for and visa versa. For this reason I'm always happy when Richmond has to wear their yellow guernsey rather than their black. But hard to measure if there's anything in it because they wear yellow for away games which would mitigate.Bias against certain teams absolutley happens but it is often completley unconcious and officials don't even notice it's happening. A study was done a few years ago going back through archival penalty data for the NHL to see if jersey color mattered in sports. These researcher's found that referees were more likley to call a penalty on a team wearing black jerseys. The example they presented was the 1979-80 Pittsburgh Penguins who changed their jerseys from sky blue to black mid-season. Before the switch, they averaged 4 penalties per game. After the switch, they averaged 6.