Trim the fronds and stalks off of the fennel bulb. Cut the bulb in half crosswise, remove the core, then thinly slice. Add the sliced fennel to a medium bowl and set aside.
Slice off the top and bottom of a blood orange so it sits flat on your cutting board. Carefully cut off the peel and pith in downward strips around the orange, removing as little fruit as possible. Carefully cut between the membranes to remove the segments. Repeat with the rest of the blood oranges, the Cara Cara oranges, and the grapefruit.
Add the citrus segments to the bowl with the fennel, along with the mint. Season with salt and toss to combine. Set aside while you make the dressing and farro.
Make the dressing: In a medium bowl, whisk together the lemon juice, honey, salt, and tarragon. Add the olive oil, a bit at a time, and whisk until fully incorporated. Set aside.
Heat a bit of olive oil in a small pot over medium heat. Add the farro and toast until just slightly golden brown. Pour in the water and bring to a boil. Reduce the heat to low, cover, and simmer for 30 minutes, until the farro is tender and has absorbed the water.
Add 2 tablespoons of the honey tarragon dressing to the warm farro and toss well.
In a small pan over medium heat, toast the pistachios until slightly brown and aromatic.
Divide the citrus fennel mixture between serving bowls and top with the farro and pistachios. Add more dressing to taste, if desired.
Nutrition - Salad, with dressing - Calories: 415, Total fat: 15 grams, Sodium: 429 mg, Total carbs: 70 grams, Dietary fiber: 11 grams, Sugars: 33 grams, Protein: 6 grams