Volumetric atmospheres work differently than standard atmospheres, there is no sky color color swatch, you adjust the sky color by playing with the color of the fog and haze settings and using the "auto decay light" sliders, grey is the default so you'll probably want to change that. Generally speaking volumetric atmospheres are best used for "early morning" and "late evening" images, daytime scenes usually look best in the standard atmospheres, mostly because the fog and haze in volumetrics have a tendency to wash the image out, and simply lowering the values makes the whole scene too dark. The best advice I can give you is to start with one of the pre-defined volumetric atmospheres, using the standard atmospheres and converting them to volumetric sometimes yields bizarre results that you don't want to have to spend the time tracking down why it's doing it (like the ocean in the far distance being black). Starting with the pre-loaded ones will allow you to experiment with the settings and see the effects, so that eventually you'll be able to create volumetric atmospheres from scratch and know what sliders and toggles will have which effects. Hope this all helps, good luck! Volumetric atmospheres are definately worth investing experimentation time.