int N = 400;

color left = color(232,154,28);   // orange
color right = color(28,232,73);   // lime green

size(N, N);

for (int x=0; x < N; x++) {
  float percent = 1.0 * x / N;  // force floating-point arithmetic
  float r = percent * red(left) + (1-percent)*red(right);
  float g = percent * green(left) + (1-percent)*green(right);
  float b = percent * blue(left) + (1-percent)*blue(right);
  stroke(r,g,b);
  line(x, 0, x, N);
}

save("colorMix1b.jpg");