start def s(a, b, s, e) { start if (s < e) { start color 0, 255 - s * 255 / e, s * 255 / e, 255; a := a + b; s := s + 1; forward a; turn 7; call s(a, b, s, e); end } end } down; call s(2, 1/100, 0, 2200); end