Metachromasia refers to the phenomenon where a tissue component stains in a different color from that of the dye used. This can result in yellow hues when a red dye is used, or purple to red shades when a blue dye is used. The presence of acid mucopolysaccharides, particularly if sulfated, causes this type of metachromasia, making it useful for detecting mucinous substances that often contain various compounds, including heavily sulfated compounds.