[jll29]

Although dogs can see violet better than humans, the sky appears blue to them like it does to us, not violet (despite violet being closer to the resonance frequency of N and O atoms).

That's because dogs only have two types of cones (color receptors) in their eyes, blue and yellow, not three as we do, so they see violet as blue.

Therefore, the sky is blue to us and to dogs, but for different reasons!