There is no such thing as an abstract machine, nor an abstract computation. If you imagine a machine adding two and two, the computation is implemented in your brain, which holds a representation of the operations. Physics is information; information is also physics. There is no information without a physical embodiment; there is no computation without physical operations.

Humans don't have infinite memory, and thus are less-powerful than Turing machines.

"Computing red": Please put more words into that phrase. It's too ambiguous to deal with.

Functions vs. algorithms: This is a good question. Can a lookup table be conscious? I said no. Therefore I must choose 'algorithm'.

A theory that explains consciousness should be statable in abstract terms using mathematical operations.

Yes, a theory that explains consciousness must explain qualia.

Answering that question would mislead people more than it would inform.