Bring 2 medium saucepans of salted water to a boil. Add the quinoa to 1 saucepan and the red rice to the other. Cover and simmer over moderate heat until tender, about 12 minutes for the quinoa and 35 minutes for the rice. Drain the grains and spread them out on baking sheets to cool.
In a medium skillet, heat 1 tablespoon of the olive oil. Add the onion, season with salt and pepper. Cover and cook over moderate heat, stirring occasionally, until golden brown, about 10 minutes. Let cool.
In a large bowl, combine the orange juice, orange zest, lemon juice, garlic and the remaining 3 tablespoons of olive oil; season with salt and pepper. Add the quinoa, rice, onion, apricots, pistachios and scallions and toss well. Serve with the arugula.
Camargue red rice is available at specialty food and health food stores. Brown rice makes an excellent substitute.