Hi there,
the update cart button inherits the GP Button colors set in the Customiser.
If you want to change that specifically then you can do this:
.woocommerce .woocommerce-cart-form .woocommerce-cart-form__contents button[name='update_cart'] {
background-color: #222;
color: #fff;
}
.woocommerce .woocommerce-cart-form .woocommerce-cart-form__contents button[name='update_cart']:hover {
background-color: #f6f7f8;
color: #222;
}
By default the button has a reduced Opacity setting until an update is made. If you want to change this then just add an opacity: 1;
property to the first rule