bicolor_fade.ino

int redPin = 3;
int greenPin = 6;
int stepDelay = 10;

void setup() {
  // put your setup code here, to run once:
  pinMode(redPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  for (int i = 0; i <= 255; i++){
    analogWrite(redPin, i);
    analogWrite(greenPin, 255-i);
    delay(stepDelay);
  }

  for (int i = 255; i >= 0 ; i--){
    analogWrite(redPin, i);
    analogWrite(greenPin, 255-i);
    delay(stepDelay);
  }
}