draw_color_square(hue){
    var gradB = this.ctx.createLinearGradient(0, 0, 0, 255);
    gradB.addColorStop(0, "white");
    gradB.addColorStop(1, "black");

    var gradC = this.ctx.createLinearGradient(0,0,255,0);
    gradC.addColorStop(0, "hsla(" + hue + ",100%,50%,0)");
    gradC.addColorStop(1, "hsla(" + hue + ",100%,50%,1)");

    this.ctx.fillStyle = gradB;
    this.ctx.fillRect(0, 0, 255, 255);
    this.ctx.fillStyle = gradC;
    this.ctx.globalCompositeOperation = "multiply";
    this.ctx.fillRect(0, 0, 255, 255);
    this.ctx.globalCompositeOperation = "source-over";
}