What is the name of the more primal (earlier evolved) color receptors in our eyes? What colors were they sensitive to?

The retina has two main types of light‐sensitive cells: rods and cones. Only the cones are involved in color vision. Mammals originally evolved with a dichromatic cone system consisting of two types of cones: 1. **Short-wavelength sensitive cones (S-cones):** These cones have an absorption peak around \(\sim420\)–\(\sim440\) nm and are most responsive to blue light. 2. **Middle-wavelength sensitive cones (M-cones):** These have an absorption peak around \(\sim530\) nm and are most sensitive to green light. In early mammalian evolution, these two cone types provided a basic (dichromatic) color vision system. Later in primate evolution, a third type of cone (the long-wavelength sensitive cone, or L-cone), sensitive primarily to red light, evolved via a gene duplication event. Thus, the more primal color receptors were the S- and M-cones, which were sensitive to blue and green wavelengths respectively.