let lineColorRed = 'red';

let lineColorBlue = 'blue';

​

function setup() {

  let canvas = createCanvas(600, 600);

  canvas.mouseOver(changeColor);

}

​

function draw() {

background(255);

 for (let i=0; i<=width; i+=150) {

    line(i,0,width-i,height);

 }

  for (let j = 150; j < height; j += 150) {

    line(0, j, width, height - j);

  }

}

​

function changeColor() {

  if (currentColor == lineColorRed) {

    stroke(lineColorBlue);

    currentColor = lineColorBlue;

  } else {

    stroke(lineColorRed);

    currentColor = lineColorRed;

  }

}