How can I eliminate the foreground and background colors of labels and keep only the underline?

[shaonianruntu]

For TODO tag, I just want to highlight it by underlining. Don't want to change its color. Is it possible to set foreground and background to null.

But when I set the style of the TODO tag as follows (without setting the foreground and background colors), it will automatically set the color of background to black, and the color of font (foreground) to white.

    "TODO": {
      "type": "text",
      "fontWeight": "600",
      "textDecoration": "underline",
    },

How can I eliminate the foreground and background colors of labels and keep only the underline?

Thanks