float z=1;
float y=1;

void setup() {
  size(400,400);
  background(0,0,0);
  ellipseMode(CENTER_DIAMETER);
  smooth();
}

void loop() {
  background(255,255,255);
  z=mouseX*255/400;
  y=mouseY*255/400;
  noStroke();
  fill(255,z,y, 255);
  ellipse(200,200, 60,20);
  fill(0,0,255, 100);
  ellipse(mouseX,mouseY, mouseX/2,mouseY/2);
  fill(0,255,0, 100);
  ellipse(mouseX,mouseY, mouseY/2,mouseX/2);
 
}