1. If using a gel-canister ice-cream maker, freeze canister overnight.
2. In a food processor, combine raspberries and 2 tablespoons of the sugar. Puree until smooth, then force through a strainer (you should have 1/2 to 2/3 cup). Discard solids. Stir together 2 tablespoons of the sugar and the lemon zest in small bowl. Stir in raspberry puree and set aside.
3. Place a large bowl and strainer on heatproof surface near stove. Combine milk and yolks in a heavy, nonstick, medium-size saucepan. Stir in remaining 1 cup sugar. Cook over medium-low heat, stirring constantly with rubber scraper, until instant-read thermometer just reaches 190 degree F, about 15 to 20 minutes (do not let boil), or until slightly thickened. Strain immediately into bowl; stir in salt.
4. Add raspberry mixture and food coloring to bowl, stirring well. Place parchment or wax paper on custard; refrigerate until chilled, about 4 hours.
5. To freeze, add cream to custard, stirring just to combine. Pour into ice-cream maker; process 30 minutes as per manufacturers directions.
6. Scrape into a 1-1/2-quart container; freeze to firm completely, about 2 hours.