Some fading, but not a good example of it.

// Not a good example.

#include "FastLED.h"
#define NUM_LEDS 40
CRGB leds[NUM_LEDS];
#define PIN 12


void setup()
{
  LEDS.addLeds<WS2812, PIN, GRB>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );
  FastLED.setBrightness(64);
}

void loop() {

  FadeInOut(0xF8, 0xF8, 0xFF);

  FastLED.show();
}


void FadeInOut(byte red, byte green, byte blue){

  float r, g, b;

  for(int k = 0; k < 256; k++) {
    r = (k/256.0)*red;
    g = (k/256.0)*green;
    b = (k/256.0)*blue;
    setAll(r,g,b);
    FastLED.delay(10);
  }

  for(int k = 255; k > 0; k--) {
    r = (k/256.0)*red;
    g = (k/256.0)*green;
    b = (k/256.0)*blue;
    setAll(r,g,b);
    FastLED.delay(10);
  }
}

void setAll(byte red, byte green, byte blue) {
  for(int i = 0; i < NUM_LEDS; i++ ) {
    leds[i].r = red;
    leds[i].g = green;
    leds[i].b = blue;
  }
}