I know this was addressed in your original thread, but too many people believe the sky is blue because “the oceans are blue”, so…
The sky is blue because it is predominantly made up of particles that are significantly smaller than the wavelengths of light passing through it. This causes the light to scatter in a way that most strongly affects smaller wavelenghts, causing blue and violet light to cascade across the sky much more frequently than yellow or red light. In Earth’s atmosphere, the largest contributor to this, both in terms of total atmospheric volume and in terms of how strongly it scatters light, is nitrogen.
Models indicate that life isn’t necessary for molecular nitrogen to exist in large quantities in the atmosphere, and that a nitrogen cycle drive by sunlight are sufficient. Moreover, any diatomic molecule that is light enough to be gaseous at even remotely livable temperatures will be small enough to cause this kind of wavelength dependent scattering that results in blue skies from light from sun-like stars.
Oceans would be super nice, but they’re not related to blue skies. Indeed, they’re a major source of water vapour, which is large enough to cause wavelength independent scattering. This type of scattering causes the sky colour to be more washed out, since it scatters white light in a way that keeps it from separating into its constituent colours.
