Toggle 3 leds (or an RGB) - mode 0 is switching pins 1-3 (Arduino / ESP32 / ESP8266)

RGB-blink-n-toggle.ino

// press and hold button for 1 second to change

const int ledRed = 0;
const int ledGreen = 1;
const int ledBlue = 2;
const int btn = 4;

int mode = 0;
int count = 0;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledRed, OUTPUT);
  pinMode(ledGreen, OUTPUT);
  pinMode(ledBlue, OUTPUT);
  pinMode(btn, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly
  int buttonState = digitalRead(btn);

  // check if the pushbutton is pressed
  if (buttonState == HIGH) {
    if (++mode > 4) mode = 0; // switch 1s,  R,G,B, White
  }

    
  switch(mode) {
    
    case 0: {
      // turn LED on:
      digitalWrite(count, LOW);

      // iterate pins 0,1,2
      if (++count > 2)
        count = 0;

      // turn LED off:
      digitalWrite(count, HIGH);
      
      break;
    }

    case 1: {
      digitalWrite(ledGreen, LOW);
      digitalWrite(ledBlue, LOW);

      digitalWrite(ledRed, HIGH);
      break;
    }

    case 2: {
      digitalWrite(ledRed, LOW);
      digitalWrite(ledBlue, LOW);

      digitalWrite(ledGreen, HIGH);
      break;
    }

    case 3: {
      digitalWrite(ledRed, LOW);
      digitalWrite(ledGreen, LOW);

      digitalWrite(ledBlue, HIGH);
      break;
    }

    case 4: {
      digitalWrite(ledRed, HIGH);
      digitalWrite(ledGreen, HIGH);
      digitalWrite(ledBlue, HIGH);
      
      break;
    }
    
  }

  delay(1000);
}

RGB-blink-n-toggle_v2.ino

// press button to change mode
// change:
//  button press: react on release
//  led: use ms to handle blinking
//  loop: do not block looping


#define delayInMs 750

/* ATTiny85
const int ledRed = 0;
const int ledGreen = 1;
const int ledBlue = 2;
const int btn = 4;
*/

/* Arduino Nano */
const int ledRed = 2; //D2
const int ledGreen = 3; //D3
const int ledBlue = 4; //D4
const int btn = 15; //A1


int mode = 0;
int count = 0;
int delaytime = 0;

bool lastBtnState = false;
unsigned long elapsedStart = 0;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledRed, OUTPUT);
  pinMode(ledGreen, OUTPUT);
  pinMode(ledBlue, OUTPUT);
  pinMode(btn, INPUT);
  digitalWrite(btn, LOW);

  elapsedStart = millis();
}

void loop() {
  // put your main code here, to run repeatedly
  int buttonState = digitalRead(btn);

  // check if the button is pressed
  if (buttonState == LOW && lastBtnState == true) {
    lastBtnState = false; 
    if (++mode > 4) mode = 0; // switch 1s,  R,G,B, White
  }
  else if (buttonState == HIGH) {
    lastBtnState = true; 
  }

  // millis > 50 days -> millis = 0 !
  // fix this to calculate a difference, if a difference is important - in this case we reset our count
  if (millis() < elapsedStart) elapsedStart = millis();

  switch(mode) {
    
    case 0: {
      if (millis() - elapsedStart >= delayInMs) {
        elapsedStart = millis();

        // turn LED on:
        digitalWrite(count, LOW);
  
        // iterate pins
        if (++count > (ledRed + 3))
          count = ledRed;
  
        // turn LED off:
        digitalWrite(count, HIGH);
      }
      break;
      
    }

    case 1: {
      digitalWrite(ledGreen, LOW);
      digitalWrite(ledBlue, LOW);

      digitalWrite(ledRed, HIGH);
      break;
    }

    case 2: {
      digitalWrite(ledRed, LOW);
      digitalWrite(ledBlue, LOW);

      digitalWrite(ledGreen, HIGH);
      break;
    }

    case 3: {
      digitalWrite(ledRed, LOW);
      digitalWrite(ledGreen, LOW);

      digitalWrite(ledBlue, HIGH);
      break;
    }

    case 4: {
      digitalWrite(ledRed, HIGH);
      digitalWrite(ledGreen, HIGH);
      digitalWrite(ledBlue, HIGH);
      
      break;
    }
    
  }
  
}