Changing the color of the character line art
I’ll change all of the line art to brown. I add a dark brown fill layer called “color” above each of the line art layers and turn on [Clip at Layer Below].
You can also change the color of the line art directly. However, by adding a clipped fill layer, it will be much easier if I want to change the color because I can easily duplicate the changed fill layer so that the new color is used for all the line art.
 Coloring the cat
I filled the cat with white earlier when hiding the paper layer, so I used that layer to create a selection range and color the body.
I simply changed the color of the fill to black.
For the ears and the paws, I make a new layer above the body layer and turn on [Clip at Layer Below] like with the ears and feathers on the girl.
Then I use the same method to create a selection area and color the cat.
I change the color of the bow tie from the color scheme to the same mint green color as the girl's costume to create a sense of harmony.
Now I’ve finished coloring both characters.
 Coloring the background
Like when coloring the characters, I’ll make selection areas from the line art and fill them with color.
Instead of grouping by parts, I’ll group by color.
Note: See parts 5 and 6 to see how I create selection areas from the line art.
For the detailed flowers, I make another two raster layers above the “flowers” layer and turn on [Clip at Layer Below].
Since this is just background, I draw some little circles in a random pattern, not drawing the flowers in detail.
I’m going to create an effect of the lights glowing against the dark blue background.
Because the yellow would blend with the blue, I choose a green color to add the glow.
I create a new layer above the blue background and paint the glow of the lights.
I use the [G-pen] or the [Brush] tool > [Opaque watercolor] brush to paint a border around the lights.
It looks like the lights are glowing dimly.
I create a new layer and paint with a brighter color.
When painting, I use the [Brush] > [Opaque watercolor] brush to blend.
Now it looks like the lights are glowing brighter. Next I’ll change the color of the line art.
I open the “line art” folder in the “background” folder, and make new layers above the “moon” and “light” layers.
I rename the layers to “h” and fill them with a lime-green or orange color, then turn on [Clip at Layer Below].
Now I’ve finished coloring all the parts.