A line is a mark with length and width, though its width is typically tiny compared to its length. Its visual qualities can give it emotional characteristics.
It is the distribution of visual weight in a work of art. It can make an artwork appear steady by being symmetrically balanced or appear uneasy by being asymmetrically balanced or uneven.
Rhythm is the repetition of visual elements to create a sense of movement in a work of art. Colors, shapes, lines, etc can be repeated to create rhythm, but as in music, variety is essential to keeping the rhythm interesting.
Colors whose relative visual temperature makes them appear seem warm. Warm colors include red, orange, yellow and red-violet. Warm colors tend to "come forward" in visual space.
Colors whose relative visual temperatures makes them appear cool. Cool colors include yellow-green, green, blue, and violet. Cool colors tend to "move back" in space.