What causes the Sun to appear yellow to observers on Earth?

The scattering of shorter wavelengths by the Earth's atmosphere

Although the Sun emits light across the entire visible spectrum, resulting in a true color of white when viewed from outside the atmosphere, it appears yellow when seen from Earth's surface. This perceived color shift is entirely due to the interaction between sunlight and the terrestrial atmosphere. The atmosphere preferentially scatters shorter wavelengths of light, such as blue and violet, across the sky, which is why the sky appears blue. Because these shorter, bluer wavelengths are removed from the direct beam of light reaching our eyes, the remaining light appears skewed towards the longer, warmer wavelengths, leading to the familiar yellow appearance.