Fix Atom Linter Underline

styles.less

// Styling Error Types
atom-text-editor.editor .linter-highlight, .linter-highlight{
  &.badge {
    border-radius: @component-border-radius;
    overflow: hidden;
    text-overflow: ellipsis;
  }
  &.error {
    &:not(.line-number){
      background-color: transparent;
      color: contrast(@background-color-error);
    }
    .linter-gutter{
      color: @background-color-error;
    }
    .region {
      border-bottom: 1px dashed @background-color-error;
    }
  }
  &.warning {
    &:not(.line-number){
      background-color: @background-color-warning;
      color: contrast(@background-color-warning);
    }
    .linter-gutter{
      color: @background-color-warning;
    }
    .region {
      border-bottom: 1px dashed @background-color-warning;
    }
  }
  &.trace, &.info {
    &:not(.line-number){
      background-color: @background-color-info;
      color: contrast(@background-color-info);
    }
    .linter-gutter{
      color: @background-color-info;
    }
    .region {
      border-bottom: 1px dashed @background-color-info;
    }
  }

  // Used by bottom status icon
  &.status-error {
    color: @background-color-error;
  }
  &.status-success{
    color: @background-color-success;
  }
}

This fixes the background color for linter errors in Atom ~1.19.0+. Removes the bright red behind text in favor of just the dashed underline. On a mac, open Atom > Stylesheet... and paste this at the bottom of the file. Save and the changes should appear.