"Chromatic" means all colors. The chromatic scale uses all twelve half-steps in the western music system. Frets are placed in the fingerboard one half-step apart. The sharp and flat signs indicate that a note has two names. For example, the note between C and D is called C-sharp (up one half-step from C) in some keys/chords, and D-flat (down one half-step from D) in others.