function setup() {
    createCanvas(400, 400);
    for (var i = 0; i < 100; i = i + 1) {
        append(x, random(width));
        append(y, random(height));
        append(changeInX, random(-3, 3));
        append(changeInY, random(-3, 3));
        append(colors, random(40, 140));
    }

    colorMode(HSB);
}

var x = [50, 70];
var y = [200, 90];
var changeInX = [3, 4];
var changeInY = [3, 7];
var colors = [40, 90];

function draw() {
    background(220);

    noStroke();

    for (var i = 0; i < x.length; i = i + 1) {
        fill(colors[i], 100, 100, 50);
        ellipse(x[i], y[i], 40);

        x[i] = x[i] + changeInX[i];
        y[i] = y[i] + changeInY[i];

        if (x[i] > width) {
            changeInX[i] = -changeInX[i];
            colors[i] = colors[i] + 10;
        }

        if (x[i] < 0) {
            changeInX[i] = -changeInX[i];
        }

        if (y[i] > height) {
            changeInY[i] = -changeInY[i];
        }

        if (y[i] < 0) {
            changeInY[i] = -changeInY[i];
        }
    }
}