You can try Mission Models 5-H Haze Grey. It is water-based, odorless, and cleans up very easily. It can be brushed or airbrushed undiluted, but doesn't cover quite as well as acrylic or lacquer-based paints (it may require several applications to cover fully, including brass photoetch parts). Also, being water-based, it won't dry as quickly, and be careful if masking over it with tape, as adherence to plastic or resin is not as strong as with the aforementioned alternates.