Bring the grapefruit juice to a boil over high heat, then reduce temperature to medium and let simmer until the liquid is reduced by about half. Remove from heat and let cool.
Once the reduced juice is cool, set up your double boiler, nesting a medium heat-proof bowl inside a medium sauce-pan filled with a couple inches of water. The water should not touch the bottom of the bowl. In the bowl, whisk together the reduced juice, eggs and yolks, sugar, pink grapefruit zest, and vanilla bean paste or vanilla extract until completely homogenized. Turn heat to high and bring water to a boil. Reduce heat to low so that the water continues to simmer. Whisk continuously until the curd thickens (25-30 minutes), then remove from heat and drop in the chunks of butter one by one, whisking each one to melt before adding the next.
Transfer curd to a bowl or jar, cover, and let cool completely. Once the curd has cooled, whisk in 1/3 cup crème fraîche and 2 tablespoons or more of the beet coloring, if desired. Whisk until completely smooth, or blend with an electric mixer.
Assemble the pie.
Pour the grapefruit curd into the gingersnap crust. Cover with plastic wrap, and refrigerate at least 4 hours.
After 4 hours, whip the cream, crème fraîche, and honey in a large bowl until soft peaks form. The whip will be slightly thicker than usual, given the richness of crème fraîche Dollop the crème fraîche whipped cream onto the center of the pie, leaving a 2-3 inch perimeter around the crust. Garnish with fresh grapefruit and zest.
Return to the fridge to set for another hour, then serve.