The best explanation I could ever come up with to explain it to students was that a color seen from a pigment is actually what it "rejects." It absorbs everything else. Something that's black absorbs all colors; That it means it absorbs "all the white." There is nothing to reflect, so it appears black. A red dress actually isn't red -- it's everything but red.
re: “rejecting” colors. I kinda like that. Great explanation.