I keep wondering... is Colin a famous literary cab driver?

Or was he just there to provide the online special features with a handy-dandy password?

Otherwise, the fact that he even has a name seems kind of out of place...

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Tragedy is when I cut my finger. Comedy is when you walk into an open sewer and die. -Mel Brooks

I don't know much about english litterature (which doesn't help to read all TN bokks), but considering Thursday seems to have growing difficulties to move inside the book World and considering the difficulties to get a cab there, I wouldn't be surprised that Colin becomes in the next books Thurday's official driver through the books.
hence the name and all the description...

I am really not sure, but there is an old UK TV programme called Dickson of Dock Green and there was a taxi driver in a few episodes of that played by a guy called Colin Rix.

This is probably not the reason, but you never know ;)

Rich