Arduino library for SK6812 based 4-channel RGBW LEDs.
The NeoPixel library from Adafruit can also be used to drive these LEDs but is larger in size and for my projects only a few of its functionalities are needed.
The function names are comparable with Neopixel.
The assembler source that drives WS2812 LEDs made by Tim ([email protected]) was used with a few modifications.
In version V1.1.0 the pulse frequency was increased from 800 kHz to 1050 khz.

void fill(RGBW RGBWColor, uint16_t FirstLed, uint16_t NoofLEDs);
void fill(uint32_t RGBWColor, uint16_t FirstLed, uint16_t NoofLEDs);
void setBrightness(uint16_t Bright);
void setPixelColor(uint16_t i, RGBW RGBWColor);
void setPixelColor(uint16_t i, uint32_t RGBWColor);
void show(void);
uint8_t getwhite(uint32_t c);
uint8_t getred( uint32_t c);
uint8_t getgreen(uint32_t c);
uint8_t getblue( uint32_t c);
uint32_t getPixelColor(uint16_t index);
uint32_t makeRGBWcolor( uint32_t Red, uint32_t Green, uint32_t Blue, uint32_t White);

1. Download zip file
   
2. In Arduino IDE: Sketch -> Include Library -> Add .ZIP Library
   
3. Include the library in your project using "#include <EdSoft_SK6812.h>" directive
   

#include <EdSoft_SK6812.h>
EdSoft_SK6812 LED(4, 5); // EdSoft_SK6812LED(NUM_LEDS, LED_PIN);
uint32_t color1 = 0X000000FF; // 0xWWRRGGBB

void setup()
{ // LED.fill(RGBWColor, FirstLed, NoofLEDs );
LED.fill(color1, 1, 5 ); // Fill LEDs 2,3 and 4 with color1
}

void loop()
{
LED.setPixelColor(0, {0, 0, 0, 255}); // Set second LED to white (using only W channel)
LED.show(); // Send the values to the LEDs
delay(500);

LED.setPixelColor(0, 0X00FF00FF); // Set second LED to white (using only RGB channels)
LED.show();
delay(500);
}

Pulse frequncy in version V1.1.0