#include <Adafruit_NeoPixel.h>

#define LED_PIN 3
#define LED_COUNT 20

Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();
}

void loop() {
  for (int i = 0; i < 256; i++) {
    for (int j = 0; j < strip.numPixels(); j++) {
      int blue = 255 - i;
      int red = i;
      int green = 0;
      strip.setPixelColor(j, strip.Color(red, green, blue));
    }
    strip.show();
    delay(10);
  }

  for (int i = 255; i >= 0; i--) {
    for (int j = 0; j < strip.numPixels(); j++) {
      int blue = 255 - i;
      int red = i;
      int green = 0;
      strip.setPixelColor(j, strip.Color(red, green, blue));
    }
    strip.show();
    delay(10);
  }
}