Looking at the Time Of Day options there is tonnes of things you can do to with to make your own custom sky the way you want. I'm aiming for a foggy morning sort of look in the mountains. But anyways here is the time of day window and the list of customizations you can do to it.
I love how much you can change this at first I thought I'd get lost in all them but they are pretty easy to follow. First of though was the get rid of the time of day changing. I want my level to be consistent and not change to lunch time in the when I want a foggy morning.
Using google for reference I searched for google mountains and the get the right sort of sky effect. The colours I was finding really stood out for me they seemed to fit what I wanted. I wanted to try get something in between these two photos with orange sky and violet fog colour.
I'm pretty happy with the way this looks but when you look up the sky dome is pure orange and looks horrible I feel like I almost want to pure a sign saying "Do not look up." But I need to change it. So I've played around with more reference and tried to go for a more bluey sky to keep the sky more realistic looking and Also trying to keep the colours too like the orange that reflects of the mountains from the sun and the purples lower down to make it seem cold. I'm pretty pleased with it I've saved the settings for both skys so I can switch back if I change my mind lately on.