// Sets the selection color to cyan
var str : String = "This is a string with \n two lines of text";

function OnGUI() {
GUI.skin.settings.selectionColor = Color.cyan;
str = GUILayout.TextArea(str);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
public string str = "This is a string with \n two lines of text";
void OnGUI() {
GUI.skin.settings.selectionColor = Color.cyan;
str = GUILayout.TextArea(str);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

public str as string = 'This is a string with \n two lines of text'

def OnGUI():
GUI.skin.settings.selectionColor = Color.cyan
str = GUILayout.TextArea(str)