How to Switch colors of an RGB LED with two Piezo-sensor

Other Hardware LEDs and Multiplexing
4

I tried to write the code more properly,

No you did not get rid of the second test like this:-

void setup ()
{
pinMode (PiezoGreen, INPUT);
pinMode (PiezoRed, INPUT);

pinMode (GreenLED, OUTPUT);
pinMode (RedLED, OUTPUT);
pinMode (BluLED, OUTPUT);
}


void loop () {

if (digitalRead(PiezoGreen) == HIGH){
  digitalWrite (GreenLED, LOW);
}
else {
  digitalWrite (GreenLED, HIGH);
}

if (digitalRead(PiezoRed) == HIGH){
    digitalWrite (RedLED, HIGH);
}
else  {
  
  digitalWrite (RedLED, LOW);
}


if (digitalRead(PiezoGreen) == digitalRead(PiezoRed))

{  
  digitalWrite (BluLED, HIGH);
}
  
  else 
{
  digitalWrite (BluLED, LOW);

}
}

Now you say:-

but then it turns the colors in the opposite way, or mix it together with the blu light)

Because that is the way you have written it.

if (digitalRead(PiezoGreen) == HIGH){
          digitalWrite (GreenLED, LOW);
// is the opposite way round to
if (digitalRead(PiezoRed) == HIGH){
    digitalWrite (RedLED, HIGH);

The blue light will only be off if one or the other Piezo is on otherwise the blue light is on if both Piezos are on or both Piezos are off.