Switching from one color to another I'm using ws2812b 2x2 LEDs and have it switching between green and red, but only one of my LEDs on my 2x2 is lighting up.
I'm using the &quot;blink&quot; FastLED sketch with Data pin 3 on my Arduino Uno, define led 4.
void loop() { 
 // Turn the LED on, then pause
 leds[0] = CRGB::Red;
 FastLED.show();
 delay(5000);
 // Now turn the LED off, then pause
 leds[0] = CRGB::Green;
 FastLED.show();
 delay(5000);
}
For changing the led color or making any other led to glow you have to put the led number instead of leds[led number]  in this case so your code will basically look like.
void loop() { 
 // Turn the LED on, then pause
 leds[0] = CRGB::Red;
 leds[1] = CRGB::Red;    
 leds[2] = CRGB::Red;
 leds[3] = CRGB::Red;
 FastLED.show();
 delay(5000);
 // Now turn the LED off, then pause
 leds[0] = CRGB::Green;
 leds[1] = CRGB::Green;
 leds[2] = CRGB::Green;    
 leds[3] = CRGB::Green;
 FastLED.show();
 delay(5000);
}

Hope this helps