I don't think that cannot do it slow.
Maybe a indexOf(":") (that is obligatory in process) can solve, or make a new method, as .style() (because of similarity with the data).
jQuery too can cache the data for speed. Example:
elem.style("color: red; top: += 1px') will store and execute as elem.animate({color: 'red', top: '+=1px'});
Then if require executes again, is more fast.
Bye.