It's hard not to mix a purple that's too strong. I'm trying to keep the cloud colors natural by dulling them down (in places) with a little warm pink or orange, and darkening them with Blue Black. But I think their basic structure is believable, at least. Next I have to go back with the light sky color around the cloud edges and here and there where it breaks through.
Sunrise Over The Cove, © 2022, work in progress (click on image for larger view)