JAVASCRIPT

mat input change placeholder color

::ng-deep .mat-input-element::placeholder{
    color: red;
}

angular material change placeholder color

.container {
  .mat-form-field-outline,
  .mat-form-field-empty.mat-form-field-label,
  .mat-form-field-label,
  .mat-form-field-underline,
  .mat-input-element,
  ::placeholder {
    color: $white !important;
  }
}