I think there's an issue with the current version of Snap and id, which is fixed in next release (0.2 which may be current by now) https://github.com/adobe-webplatform/Snap.svg/issues/166 so worth a read at some point.
However, I typically don't use an id like that for these cases, I would use 'this'. So with a handler, it can look something like...
var mySvg = Snap(400, 620);
var myRect = mySvg.rect(10,10,200,100);
var clickCallback = function(event) {
this.attr({ fill: 'blue' });
};
myRect.click(clickCallback);
jsfiddle here http://jsfiddle.net/qgTdF/2/
This solution may work for you, and be preferable, but it depends ultimately if you need to do something else (in which case maybe post another question with the specific issue). It may also be worth trying the latest version (I think 0.2), if you need to fiddle a bit and specifically use the id.