trilium/src/public/app/services/css_class_manager.js

const registeredClasses = new Set();

function createClassForColor(color) {
    if (!color?.trim()) {
        return "";
    }

    const normalizedColorName = color.replace(/[^a-z0-9]/gi, "");

    if (!normalizedColorName.trim()) {
        return "";
    }

    const className = `color-${normalizedColorName}`;

    if (!registeredClasses.has(className)) {
        // make the active fancytree selector more specific than the normal color setting
        $("head").append(`<style>.${className}, span.fancytree-active.${className} { color: ${color} !important; }</style>`);

        registeredClasses.add(className);
    }

    return className;
}

export default {
    createClassForColor
};