How to use the @nivo/sankey.SankeyDefaultProps.labelTextColor function in @nivo/sankey

controlOptions: {
            unit: 'px',
            min: 0,
            max: 60,
        },
    },
    {
        key: 'labelTextColor',
        help: 'Method to compute label text color.',
        description: `
            how to compute label text color,
            [see dedicated documentation](self:/guides/colors).
        `,
        type: 'string | object | Function',
        required: false,
        defaultValue: defaults.labelTextColor,
        controlType: 'inheritedColor',
        group: 'Labels',
    },
    {
        key: 'labelOrientation',
        help: 'Label orientation.',
        type: 'string',
        required: false,
        defaultValue: defaults.labelOrientation,
        controlType: 'radio',
        group: 'Labels',
        controlOptions: {
            choices: ['horizontal', 'vertical'].map(key => ({
                label: key,
                value: key,
            })),