#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
#include <avr/power.h>  // Required for 16 MHz Adafruit Trinket
#endif

#define PIN_NEO_PIXEL 4  // Arduino pin that connects to NeoPixel
#define NUM_PIXELS 20    // The number of LEDs (pixels) on NeoPixel

#define DELAY_INTERVAL 250  // 250ms pause between each pixel

Adafruit_NeoPixel NeoPixel(NUM_PIXELS, PIN_NEO_PIXEL, NEO_GRB + NEO_KHZ800);

void setup() {
  NeoPixel.begin();  // INITIALIZE NeoPixel strip object (REQUIRED)
}

void loop() {
  // Turn off all pixels
  NeoPixel.clear();

  // Set initial color to yellow
  int red = 255;
  int green = 255;
  int blue = 0;

  // Turn on all pixels to initial color at the same time
  for (int pixel = 0; pixel < NUM_PIXELS; pixel++) {           // for each pixel
    NeoPixel.setPixelColor(pixel, NeoPixel.Color(red, green, blue));  // it only takes effect if pixels.show() is called
  }
  NeoPixel.show();  // send the updated pixel colors to the NeoPixel hardware.

  // Change color for next cycle
  red -= 10;
  blue += 10;

  // Delay for two seconds
  delay(2000);
}