I’d say it depends on the product, and other similar products sold.

If it’s something standalone like a Christmas ornament, the colour doesn’t matter so much, especially if they didn’t notice for a year.

If it’s something that could be part of a set, then it matters a lot more.

Nevertheless, if you sent the wrong colour, you should do something to make it right. How far you should go, depends on how much the colour matters.

You could offer a full exchange of either product, if the colour is very important. Or you could offer a coupon/ % of a refund.

Whatever you do, could likely decide if this person will buy from you again in the future.