The diaphanousness of experience refers to the fact that when we inspect our experience of the world, we cannot perceive our experience itself. Instead, we only experience the world as it seems to us.
Even if we hold that naive/direct realism is false, strawberries seem red on their surfaces, and there’s nothing we can do about it.
Now, let’s compare perspectives:
The indirect realist believes he is deceiving himself. He claims to perceive an inner image of a red strawberry that he claims to be projecting outward onto the external strawberry, which he cannot actually see or apprehend directly.
Is the world really so deceitful?
The intentionalist takes diaphanousness at face value. He acknowledges that the strawberry is external to him and that he is representing it as red. He’ll happily agree that the naive/direct realist’s theory is flawed. Still, he maintains that he is representing a red strawberry in the world, not just some mental image that sits between him and the strawberry.
When the intentionalist says his experience is about the strawberry, he is saying it is about that strawberry out there in the world that seems a certain way, and not about any supposed internal image or model of it.
This preserves the common sense notion that the world is visible. When you open your eyes, you are not looking at an internal mental image of the world that sits between you and the world. You actually see the world. That is why you have eyes. Only a confused philosopher would think otherwise.
-gts