Percentage Discount?

[FinlayMg]

I'm using Dawn Theme and I wish to show a percentage saved below the image as such 

 

Like the same layout as the image, I'm aware there is code out there to do this for paid themes, however It would be great if someone could provide code for a snippet on dawn that would work

Many Thanks In Advance

Ps Info on how to change the colour to red would be amazing also.