You can pass data through an URL, it should be in the form of key/value pairs, but you shouldn't use it to pass too much data because an URL has a limit. You also should not pass sensitive information.
A key/value pair is something like this:
If you have more then one pair, you need to separate them using the & char. Here is an example:
The string after ? is called the Query String. With PHP you can easily access those key/value pairs using the super-global $_GET. So, in myScript.php you do:
$a = $GET['color1'];
$b = $GET['color2'];
Now, if you are going to create a dynamic query string, you should use urlencode() at least, so any special characters will be translated to maintain a proper URL format.