Well, I suspect, among other things, that it may have something to do with alcohol's hydroscopic properties. If you mix a cup of water and a cup of alcohol and shake it up well, you end up with less than 2 cups of liquid. Some of the water is held between the molecules of alcohol. Likely it has a similar effect on the dye. It probably holds the dye in solution well enough that it's more attracted to the alcohol than to the silicone.
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