Add the chocolate chunks to a glass bowl. Melt them in the microwave in 30-second increments, stirring between each time, until completely melted. I find it takes 2 to 3 increments.
Line a baking sheet with parchment paper. Spread the melted dark chocolate into a rectangular shape. You can make it thin or thick, depending on your preference.
While the chocolate is still wet, sprinkle the chopped pistachios, dried cranberries, and Christmas sprinkles on top. Place in the refrigerator to set for 30 minutes.
While the dark chocolate bark is setting, divide the white chocolate chips into two glass bowls. For each bowl, melt the white chocolate in 30-second increments, stirring between each time, until completely melted.
In one bowl, add about ten drops of green food coloring, and in the other bowl, add ten drops of red food coloring. Use a spatula to stir the color into the chocolate to achieve an even color. Add more or less coloring for a deeper or lighter hue.
Spread the colored white chocolate on another baking sheet lined with parchment paper in a single layer for each.
Top with Christmas sprinkles before it has time to set. Place in the refrigerator for 30 minutes to an hour to set.
Once set, remove both barks from the refrigerator and break them into pieces.
Place in a tin, serving bowl, or baggies to give to friends.