Multicolor is used when no single color covers most of the visible fabric. That includes prints such as florals, leopard, polka dots, stripes and checks; color-blocked pieces; and embroidery or appliques in several thread colors on a contrasting ground.
Construction decides which fabrics carry it. Prints need a flat surface, so they appear on microfiber, cotton jersey, satin and mesh. Lace is usually dyed as a finished piece, so most lace is one color. Two-tone lace is often the result of fiber blends: a nylon and elastane stretch lace takes dye differently in each fiber, so the elastane can stay paler than the nylon around it.
A black lace bra with a nude lining is not multicolor here; it is labelled by the lace color. The label is for pieces where the color mix is the design.