How to reset CardView background?

Question

I have a CardView which is getting colored after a button click ("reveal right answer" functionality). The card needs to get back to it's original color for the next question. I am using the default Android color, but I couldn't find the value I need to reset to (R.attr.cardBackgroundColor turns my card blue...), so I used tint like so:

@BindingAdapter("isRight", "showResult")
fun CardView.setCardTint(
    isRight: Boolean,
    showResult: Boolean,
) {
    background.setTintList(null)
    if (showResult) {
        val colorRes = if (isRight) R.color.result_right
        else R.color.result_wrong

        background.setTint(ContextCompat.getColor(context, colorRes))
    }
}

This works great, but now I need to change the colors to gradients. For that I need to go back to the original solution and change the background itself (to the gradient drawables) - and to my original problem: How to reset the CardView background to it's Android default value?