Watercolour on paper: flat pooled washes, dark rims where the pigment collected, and the tooth of the paper showing through.
First the picture is simplified into flat areas of colour, losing its fine detail the way pigment does when it settles and pools.
Then comes the choice that makes the whole thing work. The dark rims are found by looking for edges in the simplified version, not in the original. That means pigment gathers along the boundaries between washes and nowhere else. Look for edges in the original instead and every strand of hair and every speck of texture gets its own dark outline, which is not what paint does. A real wash carries water to the edge of the wet patch and leaves its pigment there, and the wet patch is a flat area of colour, not a texture.
A warm paper tint and a per-pixel grain finish it, standing in for the paper itself.