Well, for RGB colormixing I should think it best if you modify the backend.php and Arduino sketch somewhat. As it is now, php sends (depending on 'do' and 'pin') 2 bytes. The Arduino checks if the serial buffer is bigger than 2 bytes, and if it is, fetches the 2 bytes and does it's thing. One thing that dawned on me now is that I wrote "if (Serial.available() > 2)" but it should be "if (Serial.available() > 1)". After all, >2 won't trigger unless there is more than 2 bytes available, which is kinda silly as we are sending 2 byte commands.
If you want to make color-mixing, I will gladly help you with sourcecode. If you want to make a playground tutorial, Great! =D What I am thinking is to simply send 3 bytes. For colormixing you need to send 3 values of 0-255 right? Well, that is coincidentally the exact number of values covered in one byte. 
backend.php:
<?php
if(isset($_REQUEST['r']) && is_numeric($_REQUEST['r']) && isset($_REQUEST['g']) && is_numeric($_REQUEST['g']) && isset($_REQUEST['b']) && is_numeric($_REQUEST['b']))
{
$fp = @fsockopen('127.0.0.1', 1000, $errno, $errstr, 3);
if($fp)
{
fputs($fp, chr($_REQUEST['r']).chr($_REQUEST['g']).chr($_REQUEST['b']));
}
else
{
die('<b>Error('.$errno.'):</b>'.$errstr);
}
}
header('Location: index.php');
?>
That code will accept data from both a form (POST) or from the url (GET). $_REQUEST covers them both. The thought is that each color (red, green, blue) is sent to backend.php where the numeric values are replaced with their corresponding ASCII-characters using the chr()-funksjon and sent to the VB application.
Don't think you'll need to change the VB application, but the Arduino sketch needs a bit of change. Something like this:
int val;
int ledPin1 = 9;
int ledPin2 = 10;
int ledPin3 = 11;
void setup()
{
//begin the serial communication
Serial.begin(9600);
pinMode(ledPin1, OUTPUT);
pinMode(ledPin2, OUTPUT);
pinMode(ledPin3, OUTPUT);
}
void loop()
{
//check if data has been sent from the computer
if (Serial.available() > 2) {
//fetch first byte and set output (value of RED)
val = Serial.read();
analogWrite(ledPin1, val);
//fetch second byte and set output (value of GREEN)
val = Serial.read();
analogWrite(ledPin2, val);
//fetch third byte and set output (value of BLUE)
val = Serial.read();
analogWrite(ledPin3, val);
}
}
Checks if 3 or more bytes are available on the serial buffer, fetches the 3 bytes and sets values analog pins 9, 10 and 11 to the ASCII values of the 3 bytes. If you send AbC to the Arduino, pin9 will be set to 65, pin10 to 98 and pin11 to 67.