change color of dress (need dress.png file)

dress.pde

import controlP5.*;
ControlP5 ctls;

PImage img;
float bg_hue = 40.0;
float bg_sat = 0.1;
float bg_bri = 1.0;

float dress_hue = 0;
float dress_sat = 0.0;
float dress_bri = 0.0;

color bg;
void setup() {
  size(400, 800);
  colorMode(HSB, 255, 1.0, 1.0);
  prepareControlers();
}
 
void draw() {
  bg = color(bg_hue,bg_sat,bg_bri);
  img = loadImage("dress.png");
  img.loadPixels();
  for (int y = 0; y < img.height; y++)
  {
    for (int x = 0; x < img.width; x++)
    {
      int index = y * img.width + x;
      int pixel = img.pixels[index]; 
 
      float value = brightness(pixel);
      float h = hue(pixel)+dress_hue;
      if (h > 255) {
        h = h - 255;
      }
      float s = saturation(pixel)+dress_sat;
      float b = brightness(pixel)+dress_bri;

      
      if (saturation(pixel) > 0.001) {
        img.pixels[index] = color(h,s,b);
      } else {
        img.pixels[index] = bg;
      }
    }
  }
  img.updatePixels();
  background(bg);
  image(img, 0, 0);
}

void  prepareControlers() {
  ctls = new ControlP5(this);
  ctls.setColorBackground (0xdd666666);
  ctls.setColorForeground (0xdd888888);
  ctls.setColorActive (0xeecccccc);
  ControllerGroup g = ctls.addGroup("Controls",0,650);
 
  ctls.addSlider("bg_hue",   0,255, 180,  10, 10, 320,16).setGroup(g);
  ctls.addSlider("bg_sat",   0,1.0, 0.5,  10, 30, 320,16).setGroup(g);
  ctls.addSlider("bg_bri",   0,1.0, 0.5,  10, 50, 320,16).setGroup(g);
  ctls.addSlider("dress_hue",0,255, 0.0,  10, 80, 320,16).setGroup(g);
  ctls.addSlider("dress_sat",-0.5,0.5,0,  10,100, 320,16).setGroup(g);
  ctls.addSlider("dress_bri",-0.5,0.5,0,  10,120, 320,16).setGroup(g);
}