int N = 400;

size(N, N);

for (int x=0; x < N; x++) {
  for (int y=0; y < N; y++) {
    float percentX = 1.0 * x / N;
    float percentY = 1.0 * y / N;
    stroke(255*percentX, 255*percentY, 255*(1-percentX)*(1-percentY));
    point(x, y);
  }
}


save("colorMix2.jpg");