I think it is because of Duality's neutral colors, the yellow looks good. Blacks and Grey's are a good backdrop to have a yellow blade on, but when you have it outside in the bright light, the yellow loses its harshness, and somewhat disappears. That is why when the fight goes from inside to outside, it is harder to see the lightsaber unless it is contrasted against the tunics. They barely got away with it. Personally I would have used a different color, maybe Orange, but they got it in the end!