You cannot customize this style directly, as this is a bitmap / copy of what the item looked like when you started dragging:
http://jsfiddle.net/2EvGP/
EDIT:
You can actually fool to achieve this by briefly changing the style of the element when you drag and drop: http://jsfiddle.net/LULbV/
$('#draggable').bind('dragstart', function (e){ [Set style here] setTimeout(function(){ [Reset style here] }, 1); ... });
This works flawlessly in Chrome 19 and shows a style change depending on how you drag and drop Firefox 13. You will need to reset the style of the dragged item when it is deleted.
(Note that I have a pretty fast computer, so I'm not sure if this hack will work on slow machines anyway)
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