I agree, but the modern german flag breaks the ancient colour mix rules too (going back to meieval heraldry)
Colors were divided into 3 categories:
"Metals": yellow (gold), white (silver)
Practical colors: Red, Blue, Black
Less practical colors: Brown, Green, Grey etc.
The Pope was the only one allowed to break these rules. His flag was white with gold.
90% of modern flags use white/yellow as contrast or to seperate the other colors.