Hello,

Please add this custom CSS to the Theme Settings > Custom CSS > General:

.single-product-content .variations .swatches-select .text-only {
	border: 1px solid #090909;
}

.single-product-content .variations .swatches-select .active-swatch {
	background: #090909;
	color:white;
}

You need to configure text attribute swatches: https://xtemos.com/docs-topic/variable-products-and-swatches/

Best Regards