In a bowl, combine the sugars and softened butter. Mix well. Stir in each egg and then the vanilla extract until just combined. Set aside.
In another bowl, whisk together the flour, baking soda, and salt. Remove half of the mixture to another bowl (yes, a third bowl), and to this add the cocoa. Now, divide the butter mixture in half between these two bowls. Add 1/4 cup pumpkin puree and a tablespoon of greek yogurt to each. Stir until just combined.
Add the batter to a buttered loaf pan in large spoonfuls, dispersing the two colors throughout. Then use a knife to swirl the batter around.
Bake at 325°F for 50-55 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool for 5-10 minutes before removing it from the pan.