How to notify me when color is out of stock?

On my product page i have Size of the dress and colour. When the colour is out of the stock can i notify my client with custom code?
i mean, when i black box is "blocked" and user click on, i would like to add a notify div section to get their email and let me know about the dress.

The picture is an example of what i want 🙂

5 hours ago, Michalis said:

When the colour is out of the stock can i notify my client with custom code?

There is a built-in Product Waitlists feature to notify interested shoppers when sold-out products are back in stock. However, the waitlist signup option won't appear if your variants display as buttons; you need to use drop downs. 

i know, that's why i was thinking to do it with code in order dynamically pop up a message.