The Scottish smoothie knocked his pal and fellow Pop Idol Gareth Gates off the top spot with the self-penned track.
A little dig
He always said he'd be famous and now he's number one he says he's thrilled but can't resist a dig at Gareth and Will:
"Colourblind is the best way that I can thank the public for their support through Pop Idol, not by churning out a cover song, but by going in on my own."
Other new entries included Britney Spears featuring P Williams with Boys at seven.
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Darius chats to Newsround Online
Should pop stars stop doing cover versions?
Vote: Which Pop Idol will last longest?
