Actually, the syntax I thought was incorrect (with null) seems to be working -- my selector was just improperly formed, and thus yielding no elements. D'oh!
Setting the value of a style property to an empty string — e.g. $('#mydiv').css('color', '') — removes that property from an element if it has already been directly applied, whether in the HTML style attribute, through jQuery's .css() method, or through direct DOM manipulation of the style property. It does not, however, remove a style that has been applied with a CSS rule in a stylesheet or <style> element.
Obviously, I had need to remove an empty inline filter declaration so the CSS could take effect; there were other inline rules so I couldn't just remove the style attribute.