Display an image as a thumbnail and launches Thickbox for a larger view.
Sure, go to the plugin options page and edit the css file. The options page itself has some instructions about the different classes.
Head over to the options page and edit the background property of the ilc-thumb-zoom class. I've added two icons, mg.png (a gray icon) and mgblue.png (a light blue icon), just change the name of the image on the edit field.
If I get feedback that you would rather edit the css in a visual way I will remove the CSS editing and place instead a few controls to set width, height, a zoom icon path, border colors, etc. Or maybe I can enable css editing via a Advanced options tab or something, let me know what you prefer at my blog.