Hello, probably to late and I am no expert but l will offer up what I might try, though there are many roads to the same destination. I would try ultramarine blue, either burnt sienna or burnt umber to gray, and white with maybe a slight touch of turquoise deep. You might also try Payne's Gray with adding little touches of these colors. Once again, experimentation with colors is how we learn. When you do find what you like be sure to keep a record of it for future use.