I imagine that this is something already on your to-do list:
an easy way to edit the style of widgets. i would expand the javascript code snippet that is given to us by the widget editor, and have it also include the css style import tags. Then offer the css style on the website to anyone that would like to take it, but leave the default linking to the current css so that users that are not as experienced in web design could still just copy and paste.
This would allow advanced users the ability to change the location of the css styles to use, by simply uploading a css file to thier server and changing the location of the css document.
actually: a possibly better option:
include it as variables in the code. then in the javascript, use a document.write to take those variables and embed them into an on page style tag. you could then use a colorpicker, like the YUI color picker or the one by colurlovers. with some javascript to put the variables in the code.
