I will still never understand the British propensity to spell all words that have "or" sounds at the end with "our". I.e. colour, etc. It's color dammit!!![]()
'cos it isn't pronounced 'or', it's a softened 'er'. So the extra 'u' is not redundant. That said, pronunciations shift and with enough exposure to US dialects the general shift may well be to the harder US style 'color'. At which time the spelling may well follow suit.