Lionel wants to create an abstract piece of art to memorialize his grandfather, who died recently he decides that he wants it to be monochromatic which colour will best express his sorrow

In art, the color that best expresses sorrow is generally considered to be black. Black is often associated with darkness, grief, and the absence of light. It symbolizes a profound sense of loss and can effectively convey the emotions surrounding mourning and death. Thus, Lionel might consider using black as the monochromatic color in his abstract artwork to express his sorrow for his departed grandfather.