The following sketch contains various functions based on the CD77_Police_Lights_One functions, from my original sketch in GitHub, CD77_police_lights. It includes automatic color change.

CD77_police_light_one_auto_color_change.ino

/* CD77_police_light_one_auto_color_change by Chemdoc77

 Includes new functions for various number of pixels that are on in a group and for forward and reverse directions.
 Includes automatic color change with seconds input. See line 42 for this variable.
  
 ******** Version 20190203 *************

 This code is based on the police_lightsONE and police_lightsALL code:
in Funkboxing by Teldredge at:

  http://funkboxing.com/wordpress/wp-content/_postfiles/sk_qLEDFX_POST.ino

This sketch is one function from the following sketch in GitHub at:

  https://github.com/chemdoc77/CD77_FastLED/tree/master/CD77_police_lights

It uses the out of bounds concept and code from the FastLED XYMatrix Example at:

  https://github.com/FastLED/FastLED/blob/master/examples/XYMatrix/XYMatrix.ino


 */

#include "FastLED.h"

#define NUM_LEDS 24
#define Data_Pin 6


#define chipset NEOPIXEL 
#define BRIGHTNESS  40

int x = 0;  
int xx = NUM_LEDS-1;

//Timing Stuff
#define NUM_MODES 1  // note:  modes start at 0.
int landingMode = 0;  //FIRST ACTIVE MODE

//*************************************************************

int wait_ColorMode =5; // Change this number to change time each color is on.
                           // It is in seconds.    

//**************************************************************


// From the FastLED XYMatrix Example out of bounds code:

CRGB leds_plus_safety_pixel[ NUM_LEDS + 4];
CRGB* const leds( leds_plus_safety_pixel + 4);



//=============================== 
 

void setup() { 
 delay(1000); // power-up safety delay 
 FastLED.addLeds<chipset, Data_Pin>(leds, NUM_LEDS); 
 FastLED.setBrightness(BRIGHTNESS);
 FastLED.setMaxPowerInVoltsAndMilliamps(5,1500); // sets max amperage to 1500 milliamps (1.5 amps)
 set_max_power_indicator_LED(13);
 
}

void loop(){  

EVERY_N_SECONDS(wait_ColorMode){ 
  landingMode++;
if (landingMode > NUM_MODES) {landingMode = 0;}

 }

switch (landingMode) {
       case 0:cd77_police_lights_one_modified_n_dots(2, 4, 60, CRGB::Red); break; // number of dots, number of segments,  speed of animation and CRGB color.   
       case 1:cd77_police_lights_one_modified_n_dots(2, 4, 30, CRGB::Blue); break; 
                   
   }
}

//Sketch Functions  ================================

void cd77_police_lights_one_modified_n_dots(int numb_dots, int segments, uint16_t wait1, CRGB color){
 EVERY_N_MILLIS_I( ship_time, 60){ 
 ship_time.setPeriod(wait1 );
  x++;
  if (x >=  NUM_LEDS) {x = 0;}
  fill_solid(leds,NUM_LEDS, CRGB::Black); 
  for (int z=0; z< segments;z++){
  int y = x + (z*NUM_LEDS)/segments;
  if ((x + (z*NUM_LEDS)/segments) > NUM_LEDS-1) {y = (x + (z*NUM_LEDS)/segments)%NUM_LEDS; }

  
  for (int dots=0; dots<numb_dots; dots++){
  //leds[y]=   color;
  leds[y-dots]=   color;
  }
   FastLED.show(); 
     }
   }   
 }

//====================

void cd77_police_lights_one_modified_n_dots_reverse(int numb_dots, int segments, uint16_t wait1,CRGB color){
  EVERY_N_MILLIS_I( ship_time, 60){ 
 ship_time.setPeriod(wait1);
  xx--;
  if (xx <=0) {xx = NUM_LEDS-1;}
  fill_solid(leds,NUM_LEDS, CRGB::Black); 
  for (int z=0; z< segments;z++){
  int y = xx + (z*NUM_LEDS)/segments;
  if ((xx + (z*NUM_LEDS)/segments) > NUM_LEDS-1) {y = (xx + (z*NUM_LEDS)/segments)%NUM_LEDS; }

  
  for (int dots=0; dots<numb_dots; dots++){
  //leds[y]=   color;
  leds[y-dots]=   color;
  }
   FastLED.show(); 
     }
   }   
 }