sketch.js

var fixedRect, movingRect;

function setup() {
  createCanvas(800,400);
  fixedRect = createSprite(400, 200, 100, 40);
  movingRect = createSprite(200,200,100,40);
}

function draw() {
  background(255,255,255);  
  movingRect.x = mouseX;
  movingRect.y = mouseY;
  if(movingRect.x-fixedRect.x<=fixedRect.width/2 + movingRect.width/2
    && fixedRect.x-movingRect.x<=fixedRect.width/2 + movingRect.width/2
    && movingRect.y-fixedRect.y<=fixedRect.height/2 + movingRect.height/2
    && fixedRect.y-movingRect.y<=fixedRect.height/2 + movingRect.height/2){
     
    movingRect.shapeColor="Red";
    fixedRect.shapeColor="Red";
  }else{
    movingRect.shapeColor="Blue";
    fixedRect.shapeColor="Blue";
  }
  drawSprites();
}