Line a baking sheet with parchment paper. Set aside.
Place 2 chopped white chocolate bars in the top pan of a double boiler over hot but not boiling water. (You may also use a glass or metal mixing bowl on top of a saucepan half filled with water.) Allow the chocolate to melt, stirring occasionally. Remove from heat and let stand to cool for 15 minutes.
Stir remaining 1 bar of chopped chocolate into the melted chocolate. Stir until melted and smooth.
Divide melted chocolate in half. Stir matcha into half of the chocolate.
Alternately, spoon white and green chocolate onto the prepared baking sheet. Spread about 1/4 inch thick and gently swirl with a spatula. Sprinkle with salt.
Chill for 30 minutes or until firm. Use parchment to lift candy; break into pieces. Store between sheets of waxed paper in an airtight container at room temperature up to 3 days or in the refrigerator up to 2 weeks.