painting palette and render

i want to build a painting, something like this https://www.pixiv.net/member_illust.php?mode=medium&illust_id=65582627

how do i pick the color palette that is realistic?
from the image i can tell the sun and sky colour’s but for the rest, like cloths snow and treess…
how do i pick their color so that they remain within the environment’s color and not stand out?

and then, the render…
as you can see the bokeh and the brush effects…
how do i plan the variety of the shapes that will occur in the painting consistently?

thanks. this is quite urgent