Michelle,
By the way, the reason why I had to use jQuery to do this is because you can not overrive the CSS style to an element that doesn't have a uniue ID or NAME without affecting other similar elements. That's why we need to programatically select the parent LI of the field in order to change its CSS properties.
If it was not for that, we could have used a similar approach and simply use CSS to override the style. This would probably be a good enhancement to request to Marketo. To have them specify a unique ID to each row (LI) based on the field it holds.
However, at this point in time, it might not be necessary soon because the new Marketo Forms 2.0 initiative is almost ready to go live and some similar tricks could be accomplished by using the new interface. Yesterday I was lucky enough to be on a demo with Marketo with select customers on the functioning Forms 2.0 upcoming release and I can totally see things like this being easy to do with the new form editor.
Have a fantastic day!
Rafael