Hello,

The code below will help you to change the color of these labels. Please define it via Theme Settings -> Custom CSS.

.xts-product .xts-product-label {
    background-color: #5c5656;
    color: #fff;
}

.xts-product .xts-product-label.xts-onsale {
    color: #fff;
}

If there is ever anything we can do, please feel free to reach out to me anytime when you have anything more to say.

Kind Regards