Ionic 4: Style input placeholder

Use this style code:

ion-input{
    --placeholder-color: red;
    --placeholder-opacity: 1;
}

See here:https://stackblitz.com/edit/angular6-with-ionic4-list-refresh-test-yq3ntj?file=src%2Fapp%2Fapp.component.html

Please try this general styling to see if it has any effect:

::-webkit-input-placeholder { /* Chrome/Opera/Safari */
  color: red;
}
::-moz-placeholder { /* Firefox 19+ */
  color: red;
}
:-ms-input-placeholder { /* IE 10+ */
  color: red;
}
:-moz-placeholder { /* Firefox 18- */
  color: red;
}