necklace rainbow code

necklace.ino

#include <FastLED.h>

#define LED_PIN     11
#define NUM_LEDS    2
#define LED_TYPE    WS2811
#define COLOR_ORDER RGB
CRGB leds[NUM_LEDS];
#define UPDATES_PER_SECOND 100

uint8_t startIndex = 0;

void setup() {
  Serial.begin(9600);
  
  delay( 3000 ); // power-up safety delay
  FastLED.setMaxPowerInVoltsAndMilliamps(5, 500);
  FastLED.addLeds<LED_TYPE, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );

}

void loop() {
  static uint8_t startIndex = 0;
  
  startIndex = startIndex + 1; /* motion speed */ 

  FillLEDsFromPaletteColors(startIndex);
  
  FastLED.show();
  FastLED.delay(1000 / UPDATES_PER_SECOND);

}

void FillLEDsFromPaletteColors( uint8_t colorIndex)
{  
  for ( int i = 0; i < NUM_LEDS; i++) {
    uint8_t colorIdx = map(i, 0, NUM_LEDS, 0, 255) + colorIndex;
    leds[i] = ColorFromPalette( RainbowColors_p, colorIdx, 255, LINEARBLEND);
    colorIndex += 3;
  }
}