So it cannot tell the difference between different receptor strengths, such as bright blue vs dark blue, each only has a presence and an absence, like a 1-bit per channel quantized image?

Surely it could also see blue in the same place as it sees red, and then gain information from that even if it does not interpret that as purple?

If both of these were true than it would be able to see 2^12=4096 distinct 'colors' (where each is a combination of wavelengths originating from the same area)