How to style Input Placeholder Fluent UI V9 color?

[clemwo]

How can I adjust the placeholder text color in a fluent ui v9 input component?

Using the browsers inspect tool I can see it uses --colorNeutralForeground4 by default.
How can I adjust?
Setting this style for example doesn't work:

    "&::placeholder": {
      color: "blue !important",
    },

What's the best way to overwrite that?