#include <FastLED.h>
#define LED_PIN 7
#define NUM_LEDS 6
CRGB leds[NUM_LEDS];

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

void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    for (int j = 0; j < 255; j++) {
      leds[i] = CRGB(j, 0, 0);
      FastLED.show();
      delay(1);
    }
  }
  for (int i = 0; i < NUM_LEDS; i++) {
    for (int j = 0; j < 255; j++) {
      leds[i] = CRGB(0, j, 0);
      FastLED.show();
      delay(1);
    }
  }
}