Line a 9x9-inch pan with parchment paper, leaving overhang for easy removal. Stir together graham cracker crumbs, melted butter, and sugar until the texture resembles wet sand. Press firmly into an even layer using the bottom of a measuring cup. Freeze while you make the filling, at least 10 minutes.

Beat cream cheese on medium speed until completely smooth and no lumps remain, about 2 minutes. Add powdered sugar and beat until incorporated, scraping down the bowl as needed.

In a separate bowl, whip cold heavy cream to stiff peaks, about 3-4 minutes. Fold whipped cream into cream cheese mixture in two additions, keeping the mixture light and airy. Add vanilla and fold until just combined.

Transfer about one-third of the filling to a small bowl. Stir in cocoa powder, red food coloring, and vinegar until completely smooth and uniformly colored. Dollop spoonfuls of red mixture randomly over the white filling, then use a knife to swirl gently. Do not overmix - you want distinct ribbons of color.

Pour filling over chilled crust and smooth the top. Refrigerate until completely set, at least 4 hours or overnight. The center should feel firm to the touch.

Lift cheesecake from pan using parchment overhang. Run a sharp knife under hot water, wipe dry, and cut into 24 squares, cleaning the knife between cuts for neat edges. Serve chilled.