This function will clear the value of a form field (input field or textarea) when in focus (e.g "Enter your email address...") and remember the default value. If the field looses focus and the value is empty, the default value will be restored.
The function offers 2 optional parameters:
focus_color (A hexadecimal colour code to be used when the field is in focus)
blur_color (A hexadecimal colour code to be used when the field looses focus)
