sketch.js

var movingRect, fixedRect;

function setup() {
  createCanvas(800,400);
  movingRect = createSprite(20, 20, 20, 20);
  fixedRect = createSprite(400, 200, 70, 50);
  movingRect.shapeColor = "blue";
  fixedRect.shapeColor ="yellow";
}

function draw() {
  background(255,255,255);  
  movingRect.x = World.mouseX;
  movingRect.y = World.mouseY;

  if(movingRect.x - fixedRect.x < movingRect.width/2 + fixedRect.width/2 && fixedRect.x - movingRect.x < movingRect.width/2 + fixedRect.width/2 && fixedRect.y - movingRect.y < movingRect.height/2 + fixedRect.height/2 && movingRect.y - fixedRect.y < movingRect.height/2 + fixedRect.height/2){
    movingRect.shapeColor  = "red";
    fixedRect.shapeColor = "green";
  }else{
    movingRect.shapeColor = "blue";
  fixedRect.shapeColor ="yellow";
  }

  drawSprites();
}