VS Code custom color theme identifies, but does not render selected token color

Question

I am using TextMate rules to try and write a custom VSC Rust color theme that's not quite as busy as the default one, following this explanation in the docs.

For a token without semantic information, the VSC scope inspector correctly reports the color I selected (#FF0000 in the screenshot), but does not render it. Am I misunderstandings how this feature works?

My minimal settings.json snippet looks like this:

"editor.tokenColorCustomizations": {
    "[Default Dark+]": {
        "textMateRules": [
            {
                "scope": "punctuation.brackets.curly.rust",
                "settings": {
                    "foreground": "#FF0000"
                }
            }
        ]
    }
},
"editor.semanticHighlighting.enabled": false

VSC v1.71.2, rust-analyzer v0.3.1221