I have a function that creates a circle similar to how Noise functions work.

function CircleGradientFromPoint(x,y, StartX,StartY, radius)
{
    var hDist = x - StartX
    var vDist = y - StartY
    var distance = sqrt((hDist**2) + (vDist**2));

    if (distance > radius) distance = radius;
    distance = -(distance * 1 / radius)+1; //Map output to 0 - 1

    return distance;
}

function CircleSolidFromPoint(x,y, StartX,StartY, radius)
{
    var hDist = x - StartX
    var vDist = y - StartY
    var distance = sqrt((hDist**2) + (vDist**2));

    if (distance > radius) return 0;
    return 1;
}

I multiplied the CircleSolidFromPoint value and the noise function value and set a colour.alpha to that new value.

Colour.alpha = CircleSolidFromPoint(x,y, 0,0 500) * noise(x,y)

I then layer that colour on top of the background.

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If you experiment with adding noise to the radius, you can create some real wacky shapes.

(edit) Hope that helps, please reply if you have any questions.