In the first video you are using the Vegas Golden Knights home jersey. It isn't a very dark jersey, but it is darker than their white home jersey, which is why it is classified as a dark jersey in HUT. And the Golden Knights use that jersey against white jerseys in real life, so it's not something that only happens in a video game.
Every team has a home jersey and an away jersey. One of those two jerseys (usually the home jersey) is always classified as a dark jersey and the other one is always classified as a light jersey.
In the second video you are using one of the Vegas Golden Knights alternate jerseys. It is correctly classified as a dark jersey, so it is the opponent's jersey that is causing the problem in that case. After going through the collection I believe the opponent is using the Vienna Capitals black jersey from the ICE Hockey League. They seem to be the only team that has their home and away jerseys classified incorrectly. Their black jersey is classified as a light jersey even though it should be a dark jersey, and the other jersey is classified as a dark jersey even though it should be a light jersey. EA_Aljo Can you let the team know about this? And even the home/away classification might be incorrect for Vienna Capitals since the black jersey is an away jersey in the game but it seems like it should be a home jersey.
As you said, there are clear rules regarding jerseys. And in general those rules are followed very consistently. But there are some mistakes. Besides the incorrect classification of the Vienna Capitals jerseys, there are some alternate jerseys that are classified as dark jerseys even though they should be light jerseys or vice versa.