SOURCE

let c=[]
function setup(){
    createCanvas(480,480)
    noStroke()
    for(let i=0;i<72;i++){
        c[i]=random(255)
    }
}
function draw(){
    for(let i=0;i<24;i++){
        let index=i*3
        fill(c[index],c[index+1],c[index+2])
        rect(i*20,0,20,height)
    }
}