The Labour MP for Bassetlaw has launched a damning critique of his party following defeat at the general election.
John Mann blamed the loss on "a grey, monochrome representation" symbolised by the now famous Edstone.
He said Ukip managed to stand out because of its "quirkiness", while the SNP "had colour" and "a mish-mash of candidates who stood out as being, well, normal". Nick Clegg's Liberal Democrats meanwhile "descended the greasy pole even more rapidly than" they ascended.
Mr Mann was heavily critical of speeches delivered by former Labour leader Ed Miliband who he claims during a speech in Worksop said "he found things incredibly important on 18 occasions. Twice he redoubled his efforts (why were we only half trying before, some might ask)."
He referred to David Cameron's winning Conservative party as equally monochrome, but said, "Somebody had to win, so the known devil returned, because our offering was so monochrome that it appealed to nobody, not even ourselves".
Mr Mann held his seat in Bassetlaw for the fourth consecutive term with a majority of almost 9,000. Labour has held the seat since 1931.
On the future of the Labour party he blasts leadership candidates for being unable to escape what he calls their "linear" perception of politics. Their previous status as special advisors is "part of why we lost and keep losing".
"Much of Britain lives in a very monochrome world at present and we are failing to offer anything to transform this," he wrote.
Mr Mann finished the stinging assault with the rallying cry, "Colour is what we need," and pledged to reveal a "manifesto for victory [which] will colour in the blank spaces in our picture."
A Labour Party spokesman said the party will not comment on Mr Mann's letter.