#include <FastLED.h>

#define NUM_LEDS  18
#define LED_PIN   2

CRGB leds[NUM_LEDS];

void setup() {
  FastLED.addLeds<WS2812B, LED_PIN, GRB>(leds, NUM_LEDS);
  FastLED.setBrightness(200);
}

void loop() {
  fill_gradient_RGB(leds, NUM_LEDS, CRGB::Blue, CRGB::Red,  CRGB::Green, CRGB::Yellow);
  FastLED.show();
  delay(500);

}