Popes and Cardinals have been wearing red for over a thousand years. I heard one Q commentator say that Benedict 16 started this. Not true. Every pope since the middle ages has worn red shoes or red slippers. The color red signifies the blood of martyrs and their willingness to accept martyrdom (I think that’s a joke for about 99% of the Catholic hierarchy of today’s church)
The blood of the martyrs flows in the streets of Rome staining the Pope’s shoes. (Historic teaching, anecdotal)