Salient 8.5.4 is Now Compatible with Woocommerce 3.3.1 . Kindly update the Theme if you have updated Woocommerce . 

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Nectar Slider Arrows Color and Background Change

1:To Change arrow color:

.swiper-container .slider-prev > i {  color: red; }
.swiper-container .slider-next > i { color: red; }

2:To change background color:

.swiper-container a.slider-prev:hover, .swiper-container a.slider-next:hover {
    background-color: rgba(0,0,0,0.8);
}
.swiper-container a.slider-prev, .swiper-container a.slider-next {
    background-color: rgba(0,0,0,0.2);
}<p>Cheers</p>