Morocco have a red jersey, Haiti have a blue jersey, and Scotland have a blue jersey: of course all these colors would clash with Brasil's second jersey because of the dark blue color, so I don't think they are going to play any game with that jersey, at least in the group stage. By logic they should always use the yellow jersey otherwise the other teams should use the second jersey too, and it wouldn't make any sense.
They should face a team with a very light colored jersey in order to use the blue one, like England for example.
I don't understand. Why can't they use the second jersey against Morocco? One team playing in red and the other in blue makes sense for me. I understand the case with Haiti and Scotland, as they also have blue coloured jerseys. BTW, it is going to be a tough group for Brazil. Remember that they struggled during the early rounds of the CONMEBOL qualifiers. At around mid-point, they were at the 6th position. Later they improved the standings and managed to qualify for the FIFA World Cup of 2026. And they are being placed in a difficult group this time. Morocco made it to the semis last time, while Scotland is also in good form.
Because yellow against red has a better chromatic contrast than blue against red. I don't know what matches Brazil recently played against teams wearing a red jersey but I do remember that during France 1998 they played against Norway, and both teams were wearing their first jerseys as you can see in this image:

And usually national teams like to play with the first jersey, not the second like some clubs do for economical/sponsor reasons, no matter how nice the second jersey is.