There are various ways to draw shadows, such as using gray. This time, I want to add shadows as shown below.

First,

Apply the base color.

Once the base color is applied, add shadows.

Add a color darker than the base color.

Then, add an even darker shade.

Next, let's blend the colors.

Then, blend only the tips of the shadows.

Next, let's draw the lines.

It will look much better!

Now, do the same for other parts!

Complete!