I'm designing a pretty long form right now and am curious if it attracts the eye more and focuses users on filling out input fields if they're slightly highlighted if there's no values in there yet. Like this:
Browsers, by default, highlight active form elements. So I'd suggest that highlighting it certainly a common and, as such, expected UI interaction. As to whether or not you need to create your own active style, that likely depends on all sorts of factors regarding your specific project.