int redLED = 26;
int greenLED = 25;
int blueLED = 33;
int yellowLED = 27;

int lightDelay = 100;

int delayAdd = 1;

void setup() {
  Serial.begin(115200);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  pinMode(blueLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);

}

void loop() {
  digitalWrite(redLED, HIGH);
  digitalWrite(yellowLED, LOW);
  lightDelay += delayAdd;

  delay(lightDelay);

  digitalWrite(greenLED, HIGH);
  digitalWrite(redLED, LOW);
  lightDelay += delayAdd;

  delay(lightDelay);

  digitalWrite(blueLED, HIGH);
  digitalWrite(greenLED, LOW);
  lightDelay += delayAdd;

  delay(lightDelay);

  digitalWrite(yellowLED, HIGH);
  digitalWrite(blueLED, LOW);
  lightDelay += delayAdd;

  delay(lightDelay);

  if(lightDelay < 10) {
    delayAdd = 1;
  } else if (lightDelay > 100) {
    delayAdd = -1;
  }
}