Possible Duplicate:
Google Calendar API - PHP - set event’s color
How do you set/get the 'color' property for events in Google Calendar?
There is no documentation for this.
It should be a case of simply...
$event->color = "red";
like you would do if you were updating the text...
$event->title = "hello";
but the exception is saying "no such property".
This is for the PHP API Zend Gdata.
It looks like you cannot set the color of a single event through the Google Calendar GData API, according to the API documentation, even if you can do it on Google Calendar's web UI.