Believe it or not, acrylic paint sold in tubes works great for soft plastic lures. To adhere better to old plastic (not recently poured within a year), I rub some acetone on the lure's surface, let dry and paint my lures with acrylic paint, straight from the tube, not thinned with water. The paint doesn't come off!

Spike-It Chunk Paint is expensive and has a limited shelf life. It starts to glob after a year or two and the company won't tell you how to thin it. Lurecraft paint and dips are worse because of a bad seal on the bottles they come in.

Try it.

(note: if you use Spike It paint that's starting to glob up, use some PVC pipe prep to mix on some aluminum foil. It has worked for me.)