I'm not an instrument tech, but have done a fair amount of boat and house repairs. I would think an epoxy (like West System) with an appropriate powdered pigment mixed in would be the best bet. The standard West stuff is naturally fairly thin, but you can add thickeners to it to get the consistency you want. Given that you are looking at a small quantity, even the pigment itself would probably be sufficient to act as both a colorant and a thickener. Do a couple of tests first, though. West also has great technical advisors, who are basically epoxy geeks, and they are happy to take your calls and help you figure out how to use their products.
http://www.westsystem.com/ss/
http://www.westsystem.com/ss/