Gareth has pretty much covered what I'd have said. If you want a longer guide to white balancing the PD150 try my own site(posted 8441 days ago)http://www.urbanfox.tv/workbooks/sonypd150/pd150whitebal.html
or if you want a more in depth explanation - I'd highly recommend
http://www.gtc.org.uk/mainsite/zerb-a97/whitebal.htm
written by Tony Grant (freelance Cameraman)