why the sky light make the scene more yellow?

I just wanna light the shadow,what should i do?thanks in advance.

Skylight applies light to everywhere. To adjust shadows only, go to Post Process Volume>Color Grading>Shadows>Gamma>Slightly increase the 4th value.

Your skylight is set to captured scene, in this mode it lights the environment based on your scene’s background, which in this case seems yellow based on the little bit of clouds visible. If you changed your skybox/sphere the color will follow along. Or you can manually adjust it by tinting it or completely override it by adding your own custom cubemap.