Pablo picasso's guernica was created in black and white in order to:

Picasso chose to paint Guernica in a stark monochromatic palette of gray, black and white. This may reflect his initial encounter with the original newspaper reports and photographs in black and white; or perhaps it suggested to Picasso the objective factuality of an eye witness report. A documentary quality is further emphasized by the textured pattern in the center of the painting that creates the illusion of newsprint. The sharp alternation of black and white contrasts across the painting surface also creates dramatic intensity, a visual kinetic energy of jagged movement 

Symbolism creates a "hidden meaning" of some sort without obviously showing it kind of like the "ophelia among the flowers" a beautiful peace but it does not look like anything right? if you  discover  the hidden meaning being the chaos and conflicts within ones mind youll see the art as having more meaning than just flowers.