Hi,
in the tab General on your Web interface you can choose between the different events.
I think u need to first shut down your server, then choose an event, then restart your server and maybe do a dino wipe ?
I choose Easter event on our server, one with Primal Fear, and got awesome colours.
Another way is putting the event code in your GUS-ini
then u also need to stop ur server first .
Hope this helps