Marci's studies covered the mechanics of colliding bodies, epilepsy, and the refraction of light, as well as other topics. Prior to Marci, the prevailing theory of color assumed that light was modified by the action of a medium to produce color. Most theories were based upon the assumption that color was simply a modification of light varying between whiteness and blackness. Marci preceded Isaac Newton in his belief that "Light is not changed into colors except by a certain refraction in a dense medium; and the diverse species of colors are the products of refraction." Although he thought that different colors were caused by varying angles of incidence across the 1/2 degree apparent diameter of the sun, he stated that each color was condensed or disentangled from the others after refraction into homogeneous or elementary colors of red, green, blue and purple, and that no further change in color was obtained by additional refraction of elementary colors.