The idea is to fill an area by coloring the fabric behind the embroidery. Usually, this means that only the outline is embroidered, with some details added. However, tinting isn't only for coloring inside the lines. Many artists use this technique to create spectacular backgrounds, borders, and accents for their embroidery work.
If you want a clean and bold look for your picture, you can use colored markers for the color. It has a wide variety of colors and you can choose between fine tipped ones and broad tips depending on your needs. There are also refillable markers where you can just purchase ink whenever it dries up or loses its color. It's also an easy material to use. You just have to apply a single coat on the drawing. You can also add some more details using either a white colored pencil or a white inked pen.