Here's an idea - although I have to admit it probably wouldn't work with me - or Jeremy Clarkson!
To encourage people to buy fuel-efficient cars why not make those that are most environmentally-unfriendly only available in ghastly colours? How many gas-guzzlers would there be on the roads if that cool, black 4x4 were pink with purple spots?
I guess it wouldn't put off Jeremy Clarkson - who claims that he is an RSPB member by the way!