根据背景颜色更改 svg 图像的颜色

var swiper = new Swiper(".swiper-container", {
  direction: "vertical",
  slidesPerView: 1,
  spaceBetween: 30,
  autoplay: {
    delay: 3500,
    disableOnInteraction: false
  },
  mousewheel: true,
  pagination: {
    el: ".swiper-pagination",
    clickable: true
  },
  on: {
    slideNextTransitionStart: function () {
      if(document.getElementsByClassName('swiper-slide-active')[0].classList.contains('light')){
        document.getElementsByClassName('search')[0].classList.add('light-search')
      }else{
        document.getElementsByClassName('search')[0].classList.remove('light-search')
      }
    },
slidePrevTransitionStart: function () {
  if(document.getElementsByClassName('swiper-slide-active')[0].classList.contains('light')){
    document.getElementsByClassName('search')[0].classList.add('light-search')
  }else{
    document.getElementsByClassName('search')[0].classList.remove('light-search')
  }
}
  }
});

@import url("https://fonts.googleapis.com/css2?family=Lato:wght@400;700&display=swap");


/* Добавлено */
nav .light-search{
  border: none;
  border-bottom: 1px solid black;
  color: black;
}
nav .light-search::placeholder{
  color: black;
}


body {
  font-family: 'Lato', sans-serif;
  margin: 0;
}

button {
  outline: none;
  border: none;
  cursor: pointer;
}

input {
  outline: none;
}

input::placeholder {
  opacity: 80%;
  color: #fff;
}

.swiper-container {
  position: absolute;
  width: 100%;
  height: 100%;
  margin-left: auto;
  margin-right: auto;
}

.swiper-slide {
  text-align: center;
  font-size: 18px;
  background: #000;
  color: #fff;

  /* Center slide text vertically */
  display: -webkit-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  -webkit-justify-content: center;
  justify-content: center;
  -webkit-box-align: center;
  -ms-flex-align: center;
  -webkit-align-items: center;
  align-items: center;
}

.swiper-pagination {
  position: absolute;
  left: 65.4px;
}

.swiper-pagination-bullet {
  background-color: #f5f5f5 !important;
  width: 12px;
  height: 12px;
  opacity: 1 !important;
}

.swiper-pagination-bullet-active {
  background-color: #2b2b2b !important;
}

.swiper-container-vertical
  > .swiper-pagination-bullets
  .swiper-pagination-bullet {
  margin: 16px 0;
  display: block;
}

.nav {
  position: fixed;
  width: 87.5%;
  height: 36px;
  margin-top: 40px;
  display: flex;
  align-items: center;
  z-index: 9999;
}

.menu {
  width: 36px;
  height: 36px;
  margin-left: 65.4px;
  background-image: url(https://www.neir-studio.ru/img/menu_hamburger-white.svg);
  background-repeat: no-repeat;
  background-position: center center;
  background-color: transparent;
}

.logo {
  margin-left: 64px;
}

.search {
  margin-left: auto;
  background: transparent;
  padding-bottom: 8px;
  width: 400px;

  border: none;
  border-bottom: 1px solid #fff;

  font-family: "Lato", sans-serif;
  font-size: 16px;
  color: #fff;
}

.main-1 {
  position: relative;
  color: #ffffff;
  min-height: 100vh;

  background-image: url(../img/1.png);
  background-repeat: no-repeat;
  background-position: center 50%;
  background-color: #000;
  background-size: cover;
}

.main-4 {
  position: relative;
  color: #000;
  min-height: 100vh;

  background-color: #fff;
  background-size: auto;
}

.main-5 {
  position: relative;
  color: #ffffff;
  min-height: 100vh;

  background-image: url(../img/4.png);
  background-repeat: no-repeat;
  background-position: top center;
  background-color: #000;
  background-size: auto;
}

.cart-btn {
  position: fixed;
  right: 0;
  width: 120px;
  height: 100%;
  color: #fff;
  text-transform: uppercase;
  font-family: "Lato", sans-serif;

  background: rgba(34, 34, 34, 0.92);
  backdrop-filter: blur(36px);
  z-index: 9999;
}

<nav>
  <div class="nav">
    <button type="button" class="menu"></button>
    <a href="#"><img src="https://www.neir-studio.ru/img/logo-white.svg" alt="Saint Patron" class="logo"></a>
    <input type="search" name="" value="" class="search" placeholder="Search">
  </div>
</nav>
<a href="#"><button type="button" class="cart-btn">Cart (0)</button></a>

<div class="swiper-container">
  <div class="swiper-wrapper">
    <div class="swiper-slide main-1 dark">Слайд 1</div>
    <div class="swiper-slide main-4 light">Слайд 2</div>
    <div class="swiper-slide main-5 dark">Слайд 3</div>
  </div>
  <div class="swiper-pagination"></div>
</div>

<script src="https://unpkg.com/swiper/swiper-bundle.min.js"></script>