The grapefruit and tangerines can be peeled and sectioned the day before. Refrigerate them separately. The mint mixture can also me made the day before and refrigerated.
You may wonder why the mint leaves are blanched. The blanching allows the mint to retain its color - you can certainly skip this step -especially if you are making the gremolata right before serving it.
I found I preferred the salad without the simple syrup but you could easily offer it on the side if you wish.
Zest one of the grapefruits over a small bowl. Cover and set aside.
Peel and section the grapefruits and mandarins. Set aside.
Bring a small saucepan of water to a boil and fill a small bowl with ice and water. Blanch the mint leaves for about 10 seconds in the boiling water. Remove immediately to the ice water. Remove mint leaves to 2 layers of paper towel to drain. Pat the leaves until they are very dry - they will be limp!
Mince the mint leaves and place in a small bowl. Add the sugar and the 1 Tbsp. grapefruit zest.
In a platter or individual plates, divide the grapefruit and mandarin sections. Top with the pomegranate seeds and a teaspoon of the mint mixture. Garnish with additional grapefruit zest and a little simple syrup if desired.