int i= 10, c;

void setup(){
size(300, 300);
background(100);
ellipseMode(CENTER_DIAMETER);
colorMode(HSB);
//noCursor();
}

void loop(){
if(mousePressed){
fill(c, 100, i);
i++;
}
else{
fill(255);
}
ellipse(mouseX, mouseY, i, i);
}

void mousePressed(){
c= int(random(0, 255));
}

void mouseReleased(){
i= 10;
}