I think he is speaking from a empiricism perspective.
I sense Perspectival variation.
As you said with the fly, If one has an experience of seeming to see something blue, then one's sense datum is blue; equally importantly, if one is not having an experience of seeming to see something blue, then one does not have a blue sense datum.
A problem is raised by the observation because it is sometimes indeterminate what properties objects appear to us to have. To say that it is indeterminate what properties an object appears to have is to say that the object appears to instantiate some determinable, but there is no specific determinate falling under that determinable that it appears to instantiate. For example, an object might appear to fall within a certain range of colors, while there is no exact shade of color that it appears to have.
If the apparent properties of objects of perception are sometimes indeterminate, then the sense data involved would have to be metaphysically indeterminate — that is, they would have to actually lack definite characteristics. This, however, is logically impossible — an object cannot be colored but have no particular shade of color.
This sort of problem only arises when one analyzes appearance in such a way that there must always be an actual object that has all and only the properties that appear to the subject.
Correct me Fil, if that is not what you meant.
So Lustig, you are saying mental phenomena involved in perception do not have the properties that appear to us.
And Fil, you are saying that our data from the senses are alleged mind-dependent objects that we are directly aware of in perception, and that have exactly the properties they appear to have, in real life, independent of our mind.
Again, I'm just assuming this is what you guys are saying, so correct me if I'm wrong.