Hi.

Try with an atmosphere from the "Physical" collection. Those are atmospheres which should give you results similar to the real world. No need to change the volumetric color. The color of the clouds will be calculated depending on the position of the sun, as perilous7 said.

When the sun is low enough the clouds color will change. The lit parts will turn red/orange.
You can even make the look more dramatic by playing with the "Clouds Anisotropy" parameter in the "Cloud,Haze&Fog" tab. This will affect the outline of the clouds near the sun (will add a kind of glow effect).

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