Hello,
You have product images with the dark bg. Color of the wishlist icon is also dark. That’s why you don’t see dark icon on the dark bg.
In your case you may choose one of 2 workarounds:
1) Add a white text-shadow for the icon https://prnt.sc/MQUdHGg14Yy3
.product-view-default .content-product .product-image-wrapper .yith-wcwl-add-to-wishlist.wishlist-fragment .yith-wcwl-add-button a:before {
text-shadow: 2px 0px 0px rgb(255 255 255);
}
2) Add the white bg color for the wishlist icon https://prnt.sc/cZaOGYuFikVI
.product-view-default .content-product:hover .wishlist-fragment .yith-wcwl-add-button {
background-color: #fff;
}
.product-view-default .content-product .wishlist-fragment .yith-wcwl-add-button {
padding: 10px;
}
Choose one that suits your needs and add the custom to Theme Options > Custom CSS.
Regards