Your ancestry doesn't stop in Spain. During the Middle Ages, Spain did a lot of trade with Ireland, it's possible the red came from an Irish ancestor. What's also possible is that someone in your family three came from Scandinavia, or Scotland, or Britain .... both Irish and Spanish had regular contact with all of those and more for a long time, so the red could have come from any of those through the Irish ancestor as well.

We're all mutts.

No. But it is said to be more usual in Sevilla.

It is most common in Scotland at 15%and 40% with the gene.

Red hair isn't common anywhere.

You can see woman/men with a reddish tint in their hair, that is just what it is, a tint, straight from the packet!

Is red hair a common feature in Spain? If so, is there a certain area it's most common in. I ask because I have a red tint all around my beard and am the only one in my family to have it. I know that my family originally immigrated to Mexico from Spain in the late 1800's to early 1900's and have stayed in prominently Spanish communities in the north, so I'm basically trying to trace my ancestry back if that helps any?