#define LED_NUM 48
#define LED_PIN 7

#include <FastLED.h>
CRGB leds[LED_NUM];

void setup() {
  FastLED.addLeds< WS2812, LED_PIN, GRB>(leds, LED_NUM);
  FastLED.setBrightness(255);
}

void loop() {
  //FastLED.clear();
  for (int j=0; j<=15; j++){
    FastLED.clear();
    screen(j,255,0,0);
    screen(31-j,255,0,0);
    screen(47-j,0,255,0);
    FastLED.show();
    delay(200);
  }
}

void screen(int x, int r, int g, int b){
  for (int i=0; i<=0; i++){
    leds[i+x].setRGB(r,g,b);
  }  
}