let rects = 10;

let colors = [];

​

function setup() {

  createCanvas(400, 400);

   background(220);

   rectWidth = width/rects;

}

​

function draw() {

   for(let x = 0; x < rectWidth * rects; x+=rectWidth){

      for(let y = 0; y < rectWidth * rects; y+=rectWidth){

        rect(x, y, rectWidth);

      }

  }

}