Coat an 8-inch square pan with cooking spray; line bottom with parchment paper. Coat the parchment with cooking spray, and set pan aside. Put sugar, corn syrup, and 3/4 cups water in a small saucepan. Cook over medium-high heat until mixture registers 260 degrees on a candy thermometer.
Meanwhile, sprinkle gelatin over 3/4 cups water in a heatproof bowl; let stand 5 minutes to soften. Set the bowl with the gelatin mixture over a pan of simmering water; whisk constantly until gelatin is dissolved. Set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites until stiff (but not dry) peaks form. Whisk gelatin mixture into sugar mixture; with mixer running, gradually add to egg whites. Mix on high speed until thick, about 10 minutes. Add 3-4 drops of food coloring and gently fold just a few times to create streaks, be careful not to over mix. Pour mixture into lined pan and let stand until firm, at least 3 hours or overnight. Cut into squares.