If you hold a white lighter over a bowl in order to block air (while emptying the chamber of your device) repeatedly, the spot on the lighter where it was held tends to turn a yellowish colour. Also, what Left said: when you use a white lighter to pack a burning bowl, the ashes are visible on the bottom. That's why they're "bad luck", or so I'm told.

Most Bic lighters I've owned have had a white bottom anyway, so it doesn't really matter.

I, however, have never found that a white lighter carries any more bad luck than any other colour. I generally use cheap Ronson (refillable) Butane lighters. My store stocks them so I have like a million.

I'm colourblind when it comes to lighters. Fight the power!