comment.icon.theme.pcss.css

.field-icon-comment {
  color: red;
  background-image: url(../../../misc/icons/55565b/comment.svg);
}

File

core/modules/comment/css/comment.icon.theme.pcss.css

.field-icon-comment {
  color: red;
  background-image: url(../../../misc/icons/55565b/comment.svg);
}