product alerts

Hi,
I’m looking for a plugin that sends the customer an email when a new product with certain attributes is inserted.
For example:
on the site I have a
product: jeans
attribute: blue
The customer wants to be notified when the jeans product is available with a red attribute.
I searched a lot, but I haven’t found anything yet.
Would anyone know how to help me find something like this?

Davide