At the supermarket, they tend to be packaged. At the farmers' market, they're on display loose or on the vine.
I don't buy by colour: I buy by smell. No kidding -- the tomatoes on the vine bought from the speciality farm stall smell utterly different to the supermarket variety; a pungent, 'green' scent that you can pick up by sniffing the vine. The supermarket variety, even vines of tomatoes, barely smell at all when you get them out of the packaging.
And smell is a major component of the human sense of taste, conveying many of the nuances of flavour.
Is supermarket over-packaging actually an attempt to disguise the lack of aroma of foodstuffs by forcing customers to evaluate by sight rather than by the more obviously applicable sense?