It was cup-tie rules at the time...any cup, the zingari cup, the world cup...hence England's red shirt Vs W. Germany.
That's why the rs have red shorts now.
Their old white shorts clashed with, iirc, Anderlect. Home team changes...they kept them because they all though they were lucky.
They even started wearing them in the league until the League said Oi, you, No! you have to stick with the kit colours you declare at the start of the season
But they changed their official colours for the next season