Shapes that suggest forms found in nature are called Organic Shapes.
The triad and the seventh intervals forming the chord may be identified. In order to use this method, the structure of each of the different types of seventh chords should be shown. Seventh chords are four-note chords of which the pitch classes can be arranged as thirds is called a seventh chord.
According to wiki,”a tone is produced either by mixing a color with grey, or by both tinting and shading” so it’d probably be d but honestly cannot tell if that’s supposed to grey or blue
