I am unable to see the postprocess settings, it is given me a tiny picture, but worked with sky sphere settings. Well, you will need to tune that postprocess and maybe check the marketplace for a collection of postprocesses materials to apply to the volume and see if any has the features you will need. If you work with any color and change the postprocess settings you might tweak back the sky color.
Are you going to use the Deferred Render or Forward Render with your scene? This is important because you will need to check the sky material and the leaves material if they are set for Forward Render, because usually most materials follow the standard which is not Forwardshading. If what I said is sounds Im speaking greek, than dont worry, you are using the deferred render which is the standard and all materials will be fine already.
The sky provided by the BP_Sky_Sphere is very basic, there are other skies available at market place that are a lot better, but as I also sell this type of asset and to be not sounding like Im self serving with the post for a sale, I would tell you to check two sources for a nice sky material, all free from Epic:
Maybe you can also change some textures to get the look you want.