I'm commenting here from a question asked elsewhere:
Since I don't see any other info, I'm assuming the bug here is to make the drag feedback image match what the tab looks like, or is there some other look it is supposed to follow?
You can make the dragged image whatever you want using a canvas if needed using setDragImage. Removing the transparency is the bigger hurdle here.
Windows is the least flexible for this. The feedback image is drawn by a system component that applies a translucent gradient to whatever image we supply, but as far as I know, there is no means to change this appearance.
I believe Mac also applies a default translucency above the one specified by the DRAG_TRANSLUCENCY constant.
The main solution would be to add a mechanism that draws and moves a native widget(window) around following the mouse pointer, and doesn't necessarily use the native drag and drop api (or at least not entirely). A partial implementation of this exists using a <panel> element, but it doesn't work with multiple monitors with different resolutions. We probably should do this for tab dragging anyway, as it isn't really the same sort of dragging behaviour as others. But it would require quite a bit of platform-specific work.
On Linux, we follow a different codepath for tab dragging where we use a <panel> for the drag feedback like I mentioned earlier, and it does allow you to change the transparency and works on multiple screens.