Changing the stylesheets

[Kevin Bailey <..hidden..>]

Hi,

I have set up a second database to act as a copy (for training) of the 
live database.  I'm setting up a cron job to re-copy the live to the 
copy every night.

What I would like to do is to change the background colour for all the 
users when they log in to the copy site.  I need to run SQL something like:

UPDATE user_preferences SET stylesheet = 'ledger-yellow.css';

Could someone please correct my SQL and check what I want to do?

Thanks,

Kevin Bailey