Arduino ignoring serial interrupts when using FastLED

I have tried several different methods found around the internet, however none of them seem to work. This code works for cases 0-2 but when it goes into case 3 which is the rainbow chase loop, the pressing of the button does not interrupt the loop and move the counter forward. I'm assuming, as usual, I'm missing something stupid so many thanks in advance.

#define FASTLED_ALLOW_INTERRUPTS 1
#define FASTLED_INTERRUPT_RETRY_COUNT 1
#include <FastLED.h>

#define AnalogIn A0
#define SwIn 2
#define LED_Out 12
#define NUM_LEDS 5
int pushCounterz = 0;
volatile int buttonState;  // Set volatile for interrupt DO NOT SHAKE!
int lastButtonState;

CRGB leds[NUM_LEDS];

void setup() {
  // put your setup code here, to run once:
  FastLED.setMaxRefreshRate(250);
  FastLED.addLeds<WS2812, LED_Out, GRB>(leds, NUM_LEDS);
  pinMode(SwIn, INPUT);
  pinMode(LED_Out, OUTPUT);

  for (int i = 0; i < NUM_LEDS; i++) {
    leds[i] = CRGB ( 255, 0, 255 );  
  }
  FastLED.show();
  delay(120);
  for (int i = 0; i < NUM_LEDS; i++) {
    leds[i] = CRGB ( 0, 0, 0 );  
  }

  FastLED.show();
  Serial.begin(115200);
  Serial.println(pushCounterz);
  lastButtonState = digitalRead(SwIn); // Set the button state to the startup state 

  attachInterrupt((SwIn-2), button_ISR, CHANGE);  // Set SwIn button as an interrupt pin  // Change to Low???

}

void loop() {
  if (pushCounterz != 3) {
    FastLED.show();
  }
Serial.println(pushCounterz);
delay(120);
}

void button_ISR () {
    buttonState = digitalRead(SwIn);
    digitalWrite(13, buttonState);
  if (buttonState == LOW && buttonState != lastButtonState) {
    if (pushCounterz > 3) {
      //Serial.println("Reset to 0: ");
      pushCounterz = 0;
    } else {
      pushCounterz = pushCounterz + 1;
      //Serial.println("Incerment");
    }
    //Serial.println(pushCounterz);

      switch (pushCounterz) {
      case 0:
        for (int i = 0; i < NUM_LEDS; i++) {
          leds[i] = CRGB (255, 0, 0);
        }
        break;
      case 1:
        for (int i = 0; i < NUM_LEDS; i++) {
          leds[i] = CRGB ( 0, 255, 0);
         }
         break;
      case 2:
        for (int i = 0; i < NUM_LEDS; i++) {
           leds[i] = CRGB ( 0, 0, 255);
         }
        break;
      case 3:
        theaterChaseRainbow(1,50);
        break;
      default:
       for (int i = 0; i < NUM_LEDS; i++) {
         leds[i] = CRGB ( 0, 0, 0);
       }
       break;
      }
  }

lastButtonState = buttonState;
}

// Theater-style crawling lights with rainbow effect
void theaterChaseRainbow(int cycles, int speed) { // TODO direction, duration
  for (int j = 0; j < 256 * cycles; j++) {   // cycle all 256 colors in the wheel
    for (int q = 0; q < 3; q++) {
      for (int i = 0; i < NUM_LEDS; i = i + 3) {
        int pos = i + q;
        leds[pos] = Wheel( (i + j) % 255);  //turn every third pixel on
      }
      FastLED.show();

      delay(speed);

      for (int i = 0; i < NUM_LEDS; i = i + 3) {
        leds[i + q] = CRGB::Black; //turn every third pixel off
      }
    }
  }
}

CRGB Wheel(byte WheelPos) {
  if (WheelPos < 85) {
    return CRGB(WheelPos * 3, 255 - WheelPos * 3, 0);
  }
  else if (WheelPos < 170) {
    WheelPos -= 85;
    return CRGB(255 - WheelPos * 3, 0, WheelPos * 3);
  }
  else {
    WheelPos -= 170;
    return CRGB(0, WheelPos * 3, 255 - WheelPos * 3);
  }
}

Your issue is not that the button is not changing the value, but rather your code has no exit point if it does; the button will change the value, but nothing in theaterChaseRainbow tells it to stop.

Simply add a check in the method to return out if the button state changes:

// Theater-style crawling lights with rainbow effect
void theaterChaseRainbow(int cycles, int speed) { // TODO direction, duration
  for (int j = 0; j < 256 * cycles; j++) {   // cycle all 256 colors in the wheel
    for (int q = 0; q < 3; q++) {
      for (int i = 0; i < NUM_LEDS; i = i + 3) {
        int pos = i + q;
        leds[pos] = Wheel( (i + j) % 255);  //turn every third pixel on
      }
      FastLED.show();
      if (pushCounterz != 3) return; //ADDED THIS HERE*****    

      delay(speed);

      for (int i = 0; i < NUM_LEDS; i = i + 3) {
        leds[i + q] = CRGB::Black; //turn every third pixel off
      }
    }
  }
}

In addition, I would suggest simplifying your ISR to just increment the button and not have it handle the logic of the program as well. That should either be contained in the loop method or called from the loop method. This should make for some cleaner and less confusing code, as the ISR's job is simply to adjust the value of the button counter, and the loops job is to deal with the state that the program is currently in.