Willow flower consists of many smaller flowers which are collected in a large bun. The flowers themselves are so small that if they grew up on a lonely, they would not be seen on the tree.
Just right for painting outlines of the willows. In the distance they can be visualized as a ton more colors. A close range to convey the individuality of each flower.
Coloring in a raster (pixel) format. If you use a graphics editor such as adobe Photoshop, then using the fill can easily paint a picture. Outlines for coloring perfect to spend some time coloring on the computer. For children this can be fun and not an obsessive study of the work in the graphic editors, and knowledge of the world in different shades and colors.
Coloring can be printed, and then paint.