It has been proven that wearing red can confer psychological benefits ( viz my earlier post about martial arts scoring, which is referenced in the first line of the article linked above).
Clearly that doesn't mean you can bung eleven spastics in red shirts and expect them to do a job on Real Madrid.
It might, however, mean that the psychological effect of red has an impact at times which is beneficial.
It's really not that hard to understand ( although no surprise that the usual suspects seem to struggle).