WordNet sense 1 (either one of two chromatic colors that when mixed together give white (in the case of lights) or grey (in the case of pigments)):

complementary color

WordNet sense 2 (of words: having opposite meanings):

antonymous

WordNet sense 3 (acting as or providing a complement (something that completes the whole)):

complemental, completing

WordNet sense 4 (characterized or produced by addition):

additive