Плавная анимация затухания

input { 
  color: red; 
  animation-name: noValid; 
  animation-duration: 1s; 
  animation-iteration-count: infinite; 
  animation-timing-function: linear; 
} 
 
@keyframes noValid { 
  from { 
    color: red; 
  } 
  to { 
    color: black; 
  } 
}

<input type="text" name="a" value="not valid">