Painting the window
I’m going to use almost exactly the same layer painting method I used for painting the character.
1. Window frame
I create a new layer above the flat color layer and use the [Watercolor] > [Transparent watercolor], [Dense watercolor], or [Running color edge watercolor] brush to add shadows for a three-dimensional effect.
▼ Tool Used: [Running color edge watercolor]
With this tool, you can draw slightly blurred lines that look like smoke. You can use this to add an interesting texture.
I match the direction of the sunlight with the light drawn on the character’s body.
Then, I select the flat color layer for the window frame and go to the [Edit] menu > [Hue/Saturation/Luminosity] > [Hue/Saturation/Luminosity] and make the color slightly brighter.
2. Window pane
(1) I make a new layer above the flat color layer for the window pane and set it to [Clip at Layer Below]. Using the [Brush] > [Watercolor] > [Dense watercolor] brush or [India ink] > [Darker bleed] brush, I paint in the reflection of the fall leaves.
(2) I select this layer with rough colors painted in, then go to the [Filter] menu > [Blur] > [Gaussian blur], and set the area to blur to 6.0.
(3) I select this blurred layer and use the [Brush] > [Watercolor] > [Running color edge watercolor] brush to blur and blend some parts to represent the fall leaves.
Then, I go to the [Edit] menu > [Tonal Correction] > [Brightness/Contrast], and lower the [Brightness] to make the colors deeper, and slightly increase the contrast.
(4) I create a new layer and set the blending mode to [Linear burn], then darkened the right side of the window pane.
I made a new layer immediately above this and set the blending mode to [Screen] and made the left side of the glass lighter.
This makes it look like the glass is reflecting the sunlight.
I lowered the opacity of the [Screen] layer to 47%.
Note: On the left image above, I set the mode to [Normal] and put opacity to 100% to make it easier to see where I painted.
Now I’ve finished painting the window.
 Painting the classroom
Next I paint the classroom.
(1) I combine the flat color layer and the rough color layer for the classroom, then paint roughly with the [Brush] > [Watercolor] > [Transparent watercolor] or [Dense watercolor] brush.
To combine layers, go to the [Layer] palette and select the layers you want to combine, then right click and select [Combine Selected Layers] from the drop-down menu.
Note: You can select multiple layers at once by holding down the [Ctrl] key as you click.
(2) In this illustration, the classroom is the furthest away, so I will blur it to give a sense of depth.
I select the line art layer for the classroom and set it to hidden. (3) Then I select the color layer that I combined in step (1) and duplicate it by going to the [Layer] menu > [Duplicate Layer].
I blur the duplicated layer by going to the [Filter] menu > [Blur] > [Gaussian blur].
The desk right behind the character is relatively close to the foreground, so I delete that part of the blurred layer using the transparent color so that the unblurred layer beneath can be seen.
Then I make another layer on top and add some details to the desk.
Note: The left image above shows the area of the desk that was deleted on the blurred layer. The unblurred layer has been hidden to make it easier to see what was deleted.
Now I’ve finished painting the classroom.
 Adjusting the background and painting small objects
1. Painting small objects
I paint the small objects the character is holding (a leaf and a book). In the same way as the other parts, I add new layers on top of the flat color layers and turn on [Clip at Layer Below], then gradually add more layers as I paint.
2. Adjusting the window
I lower the opacity of the line art layers for the window frame and the foremost frame to about 50% to make the lines of the character stand out more.
Then I paint the wooden texture onto the window frame. I create a new layer set to [Multiply] above the shadow layer for the window frame, then use the [Transparent watercolor] brush in a small size to hand paint the wood grain.
I thought that the color was a little dark, so I reduced the opacity to 47%.
I’ve now finished painting the background. In the next part, I’ll adjust the overall colors and add some finishing touches.