I've heard the superstition too. Doesn't seem to slow down British Racing or the Irish. I too like green, tho the lime green used on many a sport bike is a bit over the top.
There's no validity to superstition (knock on wood)!!
EDIT:
I found this on the Internet, so it MUST be true!
"...Economaki is editor emeritus of National Speed Sport News, a popular weekly racing publication that has been in existence for 68 years. Economaki explained that in the 1930s and up until the end of World War II, no driver would drive a green car. 'It was a pronounced no-no in American racing,' said Economaki.
But how did this come about? 'We researched this extensively, and the only thing we could find out was that the first speedway fatality was one of the Chevrolet brothers in California who was killed in a green car. And it was the first accident that killed two drivers. Two drivers had never been killed in a racing accident before. ... That led to the superstition that green cars are bad luck.