We have a similar situation with a blue-filtered pixel. Equally, obviously, it produces no current at all when struck by red light. To further complicate this situation, in real life most colors are not pure red, pure green, or pure blue. Most colors in the world around us are a mix of them. Let's say we're taking a picture of the purple sky of twilight.
Purple light is a mix of red and blue light.
So the red-filtered pixel will let some of the purple light through, and produce a smaller electric charge than if the light were pure red. And the blue-filtered pixel will also let some of the purple light through, and also produce a smaller electric charge than if the light were pure blue. And the green-filtered pixel will let a tiny bit of the purple light through and produce an even smaller electric current because the green filter transmits some of the blue component of the purple light. As we've just stated, there's purple and there's purple. They're all purple, but they're not exactly the same purple.