I made a ws2812 (neopixel) sketch not to long ago, maybe you can use some or all of the code.
my loop only contains gw.process() for incomming messages (color, brightness, off).
I made no loops for color shows because i'm not interested in that but is should not be to difficult to adapt the code, there is however a short colorwhipe (chaser) when changing the strip color

#include <MySensor.h>
#include <SPI.h>

#include "Adafruit_NeoPixel.h"

#define NUMPIXELS 4   // Number of connected pixels on a single datapin
#define PIN 4         // Digital output pin

#define NODE_ID AUTO  //254 for testing purpose
#define CHILD_ID 0  


Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);
long RGB_values[3] = {0,0,0};

MySensor gw;

void setup()
{
    gw.begin(incomingMessage, NODE_ID, false);
    gw.sendSketchInfo("RGB Node", "1.0");
    gw.present(CHILD_ID, S_RGB_LIGHT);
    strip.begin();
    strip.show(); // Update the strip, to start they are all 'off'
}


void loop()
{
    gw.process();
}

void incomingMessage(const MyMessage &message) {
    if (message.type==V_RGB) {
  // starting to process the hex code
        String hexstring = message.getString(); //here goes the hex color code coming from through MySensors (like FF9A00)
        long number = (long) strtol( &hexstring[0], NULL, 16);
        RGB_values[0] = number >> 16;
        RGB_values[1] = number >> 8 & 0xFF;
        RGB_values[2] = number & 0xFF;

        colorWipe(Color(RGB_values[0],RGB_values[1],RGB_values[2]), 60);
     }
     
    if (message.type==V_DIMMER) {
      strip.setBrightness(round((2.55*message.getInt())));
      strip.show();
      }
      
    if (message.type==V_LIGHT) {
       if (message.getInt() == 0) {
        strip.clear();
        strip.show();
       }
    }
  
}
 
void colorWipe(uint32_t c, uint8_t wait) {
  int i;
 
  for (i=0; i < strip.numPixels(); i++) {
      strip.setPixelColor(i, c);
      strip.show();
      delay(wait);
  }
}

    /* Helper functions */

// Create a 15 bit color value from R,G,B
uint32_t Color(byte r, byte g, byte b)
{
  uint32_t c;
  c = r;
  c <<= 8;
  c |= g;
  c <<= 8;
  c |= b;
  return c;
}
   

It's not the cleanest code but it works for me...

have fun.