src/vs/editor/common/model/textModel.ts/ModelDecorationOverviewRulerOptions/_resolveColor
class ModelDecorationOverviewRulerOptions:	private _resolveColor(color: string | ThemeColor, theme: IColorTheme): string {
		if (typeof color === 'string') {
			return color;
		}
		const c = color ? theme.getColor(color.id) : null;
		if (!c) {
			return '';
		}
		return c.toString();
	}