"Impossible colors"?

Following up on our earlier discussion of the new pigment of blue, philosopher Michael Newall (Kent) calls my attention to a new paper of his.  He writes:  "My article is about another 'new' shade of blue: yellowish blue, a particular kind of impossible colour, which philosophers and scientists have traditionally viewed with suspicion. For those who'd like to see these colours, it includes some examples - I found these worked on about 70% of the subjects in my study. Anyone without institutional access is welcome to get in touch with me directly ([email protected])."