Mood, in the context of painting, usually refers to the emotional impact a piece can have on a viewer based on either the feelings expressed in the composition (such as the storytelling or subject matter) or the atmosphere used in the values (lights and darks) and color themes present in the painting.
Now, we can also use the humanized concept of "mood" to discuss this as well, such as "how did this painting make me feel?", which is still a very valid approach. In our instance, however, we'll be focusing on the mechanics of the painting itself, and leave the feelings to the viewer to sort out on their own!
To make this idea a little more tangible, let's first discuss a way we can control the color harmony and "color themes" of a piece in order to elicit a response. While we discussed basic warm-and-cool color theory in Chapter 2, Reviewing Canvas Properties and Color, I'd like to show a cool trick that Krita has in...