Author here: Yup - that's a great paper (published just after the Frontiers piece). There >are< some other organisms that have more than three photoreceptors an

Author here: Yup - that's a great paper (published just after the Frontiers piece). There >are< some other organisms that have more than three photoreceptors and seem to use them for 'proper' color vision though: many birds and fish (and perhaps some women).