void setup(){
   size(500  ,500); 
   frameRate(60);
     noStroke();
     background(204);
}

float r=128;
float g = 128;
float b =128;
float cur = 0.0;
float ang = (2.0* PI) / 60.0;
float vary = 10;

void draw(){
  fill(r,g,b);
  arc(width/2,height/2,width*5/6,height*5/6,cur,cur+ang); 
  fill(204);
  ellipse(width/2,height/2,width/2,height/2); 
   
   
   r += vary - random(2*vary);
   g += vary - random(2*vary);   
   b += vary -  random(2*vary);   
   r = constrain(r,0,255);
   g = constrain(g,0,255);
   b = constrain(b,0,255);
   cur += ang;
  
}