Arguably it could simulate itself seeing red and replace itself with the simulation.

I think the distinction between 'knowing all about' and 'seeing' red is captured in my box analogy. The brain state is a box. There is another box inside it, call this 'understanding'. We call something inside the first box 'experienced'. So the paradox hear is the two distinct states [experiencing (red) ] and [experiencing ( [understanding (red) ] ) ] are both brought under the header [knowing (red)], and this is really confusing.