Generally, when working with plastic, I sand the hell out of the surface.
In this project I skipped this step on purpose.
Using caution and proper safety hot glue some "veins" on the egg halves.
Apply primary color scheme. Add details. Dry brush with a lighter mix of the primary color.
You will see small areas where the plastic is showing through. That's what happens when you don't sand plastic and don't use a good plastic paint primer. However, in this case I wanted small areas of the plastic to show through.
Next, I put a balloon LED inside the eggs.
To go the extra mile, rig a UV LED light and fill the jar with highlighter fluid or other UV reactive liquids. Of course, you will need to make the egg water tight. That will make changing the battery a pain but it's worth it for a very neat effect.
As always, use safety gear and caution when using hot glue and working with chemicals.
Please don't put these in your mouth.