We taped acetate over the colour printouts of the tiles. We then outlined the tiles using melted chocolate on top of the acetate. The finished chocolate tiles would be easily removed from the acetate.
These nifty little icing holders dispensed the melted chocolate with no mess. They're a cool alternative to icing bags, but I'd still use a classic icing bag for very fine work and maximum control.
The chocolate outlines...
Flooding (filling) the outlines with softer, melted white chocolate, tinted with the required colours.
We used powdered tints to shade the white chocolate.