src/vs/workbench/services/themes/common/colorThemeData.ts/ColorThemeData/getTokenColorIndex
class ColorThemeData:	private getTokenColorIndex(): TokenColorIndex {
		// collect all colors that tokens can have
		if (!this.tokenColorIndex) {
			const index = new TokenColorIndex();
			this.tokenColors.forEach(rule => {
				index.add(rule.settings.foreground);
				index.add(rule.settings.background);
			});

			this.semanticTokenRules.forEach(r => index.add(r.style.foreground));
			tokenClassificationRegistry.getTokenStylingDefaultRules().forEach(r => {
				const defaultColor = r.defaults[this.type];
				if (defaultColor && typeof defaultColor === 'object') {
					index.add(defaultColor.foreground);
				}
			});
			this.customSemanticTokenRules.forEach(r => index.add(r.style.foreground));

			this.tokenColorIndex = index;
		}
		return this.tokenColorIndex;
	}