I got this idea from a AccioLacquer's blog post, this is my interpretation of this, and how I made these 'eggs'.
What I used:
Polystyrene Egg - 78mm
Black Acrylic Paint
200-250 Push Pins / Drawing Pins / Tacks
Black Polish - Jess Midnight
Duochrome Polish - W7 Twilight
First thing I did was to roughly paint the foam egg black, so that any gaps with the pins wouldn't show through.
Then I pushed pins in to a box, in lines so that I knew where I was up to rather than it being random
Painted the pin heads with the black polish
Second coat of black polish
Paint the pin heads using a duochrome polish, then top coat the pins
Begin sticking the pins in the egg, starting at the bottom in a spiral formation up to the top, over lapping the previous pin to keep it in place
Glue gun the last pin in place, and your egg is complete!