sketch.js

var fixedRect,movingRect;

function setup() {
  createCanvas(800,400);
 fixedRect = createSprite(400, 200, 50, 50);
fixedRect.shapeColor = "green";

 movingRect = createSprite(400, 200, 70, 30);
movingRect.shapeColor = "green";
}

function draw() {
  background(0);  
  movingRect.x = mouseX;
  movingRect.y = mouseY;

  if(movingRect.x-fixedRect.x<movingRect.width/2+fixedRect.width/2 && 
    fixedRect.x-movingRect.x<movingRect.width/2+fixedRect.width/2 &&
    movingRect.y-fixedRect.y<movingRect.height/2+fixedRect.height/2 && 
    fixedRect.y-movingRect.y<movingRect.height/2+fixedRect.height/2 ){

      movingRect.shapeColor = "red";
      fixedRect.shapeColor = "red";
  }
  else{
    movingRect.shapeColor = "green";
    fixedRect.shapeColor = "green";
  }


  drawSprites();
}