Step 6: Paint
Then I gave each block a couple of coats of primer, sanding with 240grit after each coat.
I went for the "Tetris worlds" colour scheme...as all the other versions have a magenta (pink!) block. I thought I'd give spray paint a chance as I found it hard to get a smooth finish with brushes on my first set.
Spray paint was virgin territory for me, so I checked out this instructable.
Basically....spray at about 6inches & perpendicular to the surface, wear a good quality mask, and it's better to do lots of thin coats instead of fewer thick coats.