int red=2;
int green=3;
int blue=4;
String myColor;
String msg="choise your color from following (r,g,b)";
void setup() {

Serial.begin(9600);
pinMode(red,OUTPUT);
pinMode(green,OUTPUT);
pinMode(blue,OUTPUT);
}

void loop() {
 Serial.println(msg);
 while(Serial.available()==0){


 }
  myColor = Serial.readString();
  myColor.trim();
  myColor.toLowerCase(); 
 if(myColor=="r"){
    analogWrite(red, 255);
    analogWrite(green, 0);
    analogWrite(blue, 0);
 }
 if(myColor=="g"){
    analogWrite(red, 0);
    analogWrite(green, 255);
    analogWrite(blue, 0);

 }
 if(myColor=="b"){
    analogWrite(red, 0);
    analogWrite(green, 0);
    analogWrite(blue, 255);
 }

}