"... when hung from the lampposts of San Francisco the pole would block the middle colour, so they deleted one to leave an even number so none of the colours (each representing a value or meaning) would be obscured."
Wouldn't that imply that one "value or meaning" was ditched for the sake of appearances? (And if that really was the case, which one?) Why not add another colour representing another value or meaning? There are plenty of both.
Besides, the "problem" would be strictly one-sided, so to speak... and fixing it by removing one stripe would result in the the pole blocking 1/2 of two colours each.
Strong whiff of "meaningful explanation added to coincidence after the fact".
No, I guess someone just found another supplier of flags that were more attractively priced, but had six colours.