// Arduino Nano/Uno with one WS2812

#include <FastLED.h>                // https://github.com/FastLED/FastLED
#define PIX 1                       // number of WS2812
#define PIN 6                       // data pin

CRGB led[PIX];                      // Create FastLED object (led[])

int maximum = 255;                  // adjust maximum brightness
bool toggle;                        // a bit to toggle
unsigned long timer, timeout = 500; // timer

void setup() {
  FastLED.addLeds<WS2812, PIN, GRB>(led, PIX); // initialize object
  FastLED.clear();                             // clear buffer
  FastLED.setBrightness(maximum);              // set brightness
  FastLED.show();                              // display buffer
}

void loop() {
  if (millis() - timer >= timeout) {
    timer = millis();                  // reset timing
    led[0] = CRGB(0, 0, 255 * toggle); // send color to buffer
    FastLED.show();                    // show buffer
    FastLED.clear();                   // clear buffer
    toggle = !toggle;                  // toggle on/off multiplier
  }
}