BLEND_ADD
BLEND_ADD(p, color.red, color.green, color.blue, *covers);
BLEND_ADD(p, colors->r, colors->g, colors->b, *covers);
BLEND_ADD(p, colors->r, colors->g, colors->b, cover);
BLEND_ADD(p, color.red, color.green, color.blue, cover);
BLEND_ADD(p, color.red, color.green, color.blue, cover);
BLEND_ADD(p, color.red, color.green, color.blue, *covers);