Depends on what you are going to do with it. If you plan to print it, the white is probably better - cleaner and uses less ink/toner. if you plan to display it on a webpage then its up in the air and might also have some dependency on the color of the chip itself (white chip on a white background sometimes loses its edges). But finally it depends on personal preference. Of course you can save it as .GIF and use a transparent background so it will be whatever is behind that.