С помощью css перекрасить png в белый

body{ 
background: mediumpurple 
} 
 
img { 
  width: 300px; 
} 
 
.white { 
  filter: grayscale(1) brightness(1000%); 
} 
 
.black { 
  filter: brightness(0); 
}

<img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png?v=9c558ec15d8a"> 
<img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png?v=9c558ec15d8a" class="white"> 
<img src="https://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-logo.png?v=9c558ec15d8a" class="black">

.img-container { 
  position: relative; 
} 
 
.img-container:after { 
  position: absolute; 
  content: ''; 
  display: block; 
  top: 0; 
  left: 0; 
  right: 0; 
  bottom: 0; 
  background: rgba(255, 255, 255, .75); 
}

<div class="img-container"> 
  <img src="http://placehold.it/600x400" /> 
</div>