Possibly because it was a "friendly" it was allowed to slide. I suspect had it been a UEFA competition, one of the teams would have had to change.
What is and isn't allowed seems to go in phases. Wasn't that long ago in a lot of leagues Blue vs Burgundy for example was a no go. In recent years there has been an increased awareness that more needs to be done to help those that are colour blind.
A few years ago, I posted a picture on here on Stoke vs Huddersfield where both sides were wearing Red/Blue & White striped shirts with white shorts and suggested it was a colour clash, to which many on here laughed at. Easy to say when you don't suffer from colour blindness, are we really going to potentially exclude people from being able to watch a game simply because "I'm alright jack, stuff everyone else"?