Yeah, I'd thin with Future - and consider getting a flow aid. Liquitex makes one called Flo-Aid which reduces the surface tension, and they make a drying retarder called Slo-Dri which you may not really need here.
Increasing the alcohol will make it dry faster, for this I don't know if I'd add alcohol. It can cause the Future to haze a little but usually not to any great degree.
If you screw it up, just drop the part into Windex and clean it off. I've tinted canopies this way: Future with water/alcohol/flow-aid/India Ink/pearl powder. I dipped 2 or 3 times to get the hue I wanted. I had to strip the parts after my masking/frame painting didn't work right a total of 3 times! The fourth time worked.
Of course the canopy parts were not attached to the model here...which made that process much more simple.
That was for these kits:
http://www.starshipmodeler.com/other/tm_exyamato.htm
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