Sand down the tip where the nipple of the balloon made a non-egg like mark.
Give it some more time to dry without the balloon.
You are ready to decorate.
Let your imagination run wild here. Spray paint works. You might try a primer coat to make it smoother, less porous. I want to try painting it, covering part with masking tape and painting a gain to get stripes. In the pictures I just painted it Silver and Pink.
I really like the metallic colors. Gold has worked nicely. And there is the nice imagery of the Golden Egg.
I'd love some ideas on decorating, this is not my strong suit.
Check out the painter pyramid instructable I did www.instructables.com/id/Painters-Pyramid-cardboard-version/