Arduino/Processing SerialTest

ArduinoSerialTest.ino

int colour = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  colour = (colour + 1) % 255;
  Serial.println(colour);
  delay(10);
}

ProcessingSerialTest.pde

import processing.serial.*;
Serial myPort;
String sensorReading="";

int colour = 0;

void setup(){
  size(600,600);
  
  myPort = new Serial(this, "/dev/ttyACM0", 9600);
  myPort.bufferUntil('\n');
}

void draw(){
  background(colour, colour, colour);
}

void serialEvent (Serial myPort){
  sensorReading = myPort.readStringUntil('\n');
  if (sensorReading != null){
    sensorReading=trim(sensorReading);
    colour = Integer.parseInt(sensorReading);
    println(colour);
  }
}