int barWidth = 5;
  int[] brightness;
  
  void setup() 
  {
    size(200, 200);
    colorMode(HSB, 360, height, height);  
    brightness = new int[width/barWidth];
  }
  
  void draw() 
  {
    int j = 0;
    for (int i = 0; i <= (width-barWidth); i += barWidth) {  
      noStroke();
      if ((mouseX > i) && (mouseX < i+barWidth)) {
        brightness[j] = mouseY;
      }
      fill(i, height, brightness[j]);
      rect(i, 0, barWidth, height);  
      j++;
    }
  }