Is it ever appropriate to wear a gold lamé kittel? As far as I know, there were no holidays this weekend (Sept. 9 - 10), but I spotted someone in a pale gold lamé kittel that would have looked more appropriate in Las Vegas than Forest Hills, but what do I know? is there some kind of minhag for when it's appropriate and when not?
I assume you're referring to men.
It's customary to wear a white Kittel all night and day on Yom Kippur - source Kitzur Shulchan Aruch 131
נוֹהֲגִין לִלְבּוֹשׁ אֶת הַקִּיטֶל, שֶׁהוּא בֶּגֶד מֵתִים, וְעַל יְדֵי זֶה לֵב הָאָדָם נִכְנָע וְנִשְׁבָּר.
Some also do so on Rosh Hashana during the day. (And some wear it all day on Rosh Hashana too)
On Shabbat Chazon some have the custom not wear their regular Shabbat clothes - (ibid 122)
אֲבָל שְׁאָר בִּגְדֵי שַׁבָּת, תַּלְיָא בְּמִנְהַג הַמְּקוֹמוֹת אִם לְהַחְלִיפָן אוֹ לֹא
Any other week one is supposed to get dressed in nice clothes for Shabbat (ibid 72). A gold lamé kittel would surely qualify.
יִשְׁתַּדֵּל שֶׁיִּהְיוּ לוֹ בְּגָדִים נָאִים, וְגַם טַלִּית שֶׁל מִצְוָה נָאָה לִכְבוֹד שַׁבָּת, דִּכְתִיב וְכִבַּדְתּוֹ, וְדָרְשִׁינָן, שֶׁלֹּא יְהֵא מַלְבּוּשְׁךָ שֶׁל שַׁבָּת כְּמַלְבּוּשְׁךָ שֶׁל חֹל