SOURCE

let h=120;
let pointY=20;
function setup() {
  createCanvas(1000,1000);
  colorMode(HSB,300,300,100);
}

function draw() {
    if(keyIsPressed){
        if(key=='Q'){
            h-=1;
        }
        else if(key=='W'){
            h+=1;
        }
        else if(key=='A'){
            pointY-=0.5;
        }
        else if(key=='S'){
            pointY+=0.5;
        }
    }

if(mouseIsPressed){
    stroke(h,100,100);
    strokeWeight(pointY);
    line(mouseX,mouseY,pmouseX,pmouseY);
     }
}

<script src='https://cdn.jsdelivr.net/npm/p5@1.1.9/lib/p5.min.js'></script>