Seeking a different kind of 'Recommend' function by Gil Kruger

I've noticed Shopify sites like TheChivery have a pop-up that suggests an alternate product variant when the one selected is out of stock.

Have searched high and wide for an app like this - basically, want a pop-up box that essentially says to the customer:  "Sorry this t-shirt is out of stock in this color, but we have another color available in your size"  

Does such a thing exist?

Thanks so much,

Gil