Hello,

I inspect your site as on hover you have selected the white color from theme settings that’s why on the shop page on the product grid items, the add to cart button display in white background and your dark text color not applying on it because it is an icon not the text.

If you want to display that cart icon in black with hover effect then use the below CSS code in global custom CSS area under theme settings>> custom CSS:

.woodmart-hover-base:not([class*=add-small]) .wd-bottom-actions .add-to-cart-loop:before {
   color: black;
}

Best Regards.