Why play games?

Go harvest a bunch of poison ivy. Chop and mash the stalks and leaves, then press into a jar. Fill the remaining jar space about 1/2 full of grain alcohol or strong gin or vodka. Shake and let it sit in cool, dark place. Shake jar daily.
3 weeks, use a strainer to pour off the infused alcohol liquid into smaller jar. Press the leaves and stems to get the good juices out, then discard those.

You now have a mixture containing urushiol (the active compound in poison ivy). You can now mix THAT with black paint and fill those water balloons.