To make this follow the instructions on your package of long grain rice, the trick is to replace the water with chicken stock. Cooking this way gives some needed flavor to the rice and also helps to keep it moist while cooking.
I had decided that a pre-made black gel food dye would be best and headed to the store while the rice cooked. I spotted some rice noodles and found the translucent color and slippery texture interesting so I decided to dye those as well.
I added the dye to both the rice and noodles while they were warm and then let them cool down over night. It ended up taking a surprising amount of gel dye to get the color to show (probably half a Tablespoon for a half a cup of starch).
In the end I think the rice noodles turned out better for Halloween. The vaguely see-through quality they have worked well with the paler colors, they could pass for a "bowl of worms" at a party. But the rice was pretty darn tasty.