SOURCE

let h=180;
let point=10;
function setup() {
    createCanvas(500,500);
    colorMode(HSB,360,100,100);
}

function draw() {
    if(keyIsPressed){
        if(key=='q'){
            h-=1;
        }
        else if(key=='w'){
            h+=1;
        }
        else if(key=='a'){
            point-=0.2;
        }
        else if(key=='s'){
            point+=0.2;
        }
    }
    if(mouseIsPressed){
        strokeWeight(point);
        stroke(h,100,100);
        line(mouseX,mouseY,pmouseX,pmouseY);
    }
}

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