a steiner answer (lol):
lazure painting (or close) in blues to be the sky, the green will be the grass, and there you have it.
now, lazure takes a bit of time (days sometimes), and it is it's own technique with it's own special brushes, workshops, ways of mixing the paints (stockmar watercolor pigments put into an acrylic matte medium with an addition of a thinner so that it dries slowly and can be applied in thin layers), and is just overwhelming to even think about.
but, you can do "faux-lazure" which a friend of mine and I did in her yoga room. essentially, we just got very large, soft paint brushes (the largest we could find), and then got regular room paints in the same hue value (i think it was second above the white-color one on one of those paint thingies that show from light to dark paint options), in the colors that she wanted. she wanted the room to be blues and violets like just after the sun went down (twilight), and so we got a bunch of those (probably 4-6 colors).
we painted the whole room a base coat of a light blue, and then began to add (as quickly as possible since it would dry), layers of the other paint colors. we would just move it and layer it on and there it went and it was lovely. i would go with sunny blues and perhaps some whispy whites for clouds, and some darker blues now and again, and perhaps a bit of yellow in a given corner for the sun.
i don't know. something fun and natural.