Neopixel LED colour control via potentiometer

neopixel.ino

// Arduino code for Neopixel LED controller
// using a potentiometer and switch button
// (C) Ismail Uddin, 2015
// www.scienceexposure.com

#include <Adafruit_NeoPixel.h>
#define PIN 3
Adafruit_NeoPixel strip = Adafruit_NeoPixel(12, PIN, NEO_GRB + NEO_KHZ800);

int potPin = 2;
int val = 0;
int colorVal = 0;
int reading = 0;
int x;
int prevVal = 0;


void setup() {
  // put your setup code here, to run once:
  strip.begin();
  strip.show();

}

void loop() {
  // put your main code here, to run repeatedly:
  reading = analogRead(potPin);
  colorVal = (reading/1024.0) * 255;
  
   
   // Neopixel Color code
   for (x=0; x < prevVal; x++)
   {
     strip.setPixelColor(x,colorVal,0,255-colorVal);
     strip.show();
   }
  }
}

Thank , it is what i did finally, and it work.