Is it permissible on Shabbat to polish one's shoes, and would there be a distinction in this regard between color and clear polish?
Polishing shoes on Shabbat transgresses the Torah prohibition of Tzovei'a, dyeing on Shabbat. When Benei Yisrael constructed the Mishkan, they dyed animal skins to be used as curtains in the Mishkan. The Talmud Yerushalmi in Perek Klal Gadol, Halacha 2, tells that they would dye the skins by beating the animal so that blood would form in between the skin and the flesh. This establishes the Melacha (forbidden activity) of Tzovei'a, which forbids coloring materials – such as shoes – on Shabbat. This includes all types of shoe polishing, even with clear polish.
The Torah prohibition of Tzovei'a applies specifically to applying a permanent dye, and the Sages later enacted a prohibition against applying even temporary dye (Rambam, Hilchot Shabbat 9:13). It would thus seem, at first glance, that polishing shoes, which has but a temporary coloring effect, is forbidden on Shabbat only on the level of Rabbinic enactment. In truth, however, this prohibition obtains even on the level of Torah law. When a person polishes his shoes, his hope is that the polish remains on the shoe permanently, and, what more, the polish in and of itself is capable of remaining permanently on the shoes. The fact that the shoes' wear-and-tear and exposure to the elements naturally fades their color does not render the polishing temporary, because intrinsically, its effect is permanent. Therefore, polishing one's shoes on Shabbat transgresses the Torah prohibition of Tzovei'a. (Menuhat Ahava, Helek 3, page 6)
It should be noted that even buffing one's shoes with a dry cloth would be forbidden on Shabbat, given the whitening effect is has on the shoes (ibid).
A fundamental rule relevant to Tzovei'a establishes that this prohibition does not apply to foods or beverages. (See Shulchan Aruch, Orach Hayim, siman 320:19, and Yichaave Daat 6:23.) Therefore, Halacha allows placing a teabag in hot water (provided that no violation of Bishul – cooking – is involved), despite the consequent coloration of the water. This applies as well to adding colored spices to foods or drinks; since these spices are added for taste, and not for coloring, no prohibition is involved.
Tzovei'a does apply, however, when one mixes foods or beverages specifically for the purpose of color. Therefore, if a person wishes to use white wine for Kiddush, he may not add some red wine to change its color for the purpose of satisfying the requirement to use red wine for Kiddush. Since in this case one mixes the wines specifically for the purpose of coloration, the mixing is forbidden due to the prohibition of Tzovei'a. (Menuhat Ahava, Helek 3, page 17.) See Halichot Olam, Helek 4, page 280, that is lenient to add red wine to whit wine.
Summary: One may not polish shoes on Shabbat with colored or clear polish, or buff his shoes with a dry cloth. One may mix foods or beverages together or add spices to a food or beverage, even if this results in the coloration of one of the foods or beverages, provided that he does so for the purpose of taste. One may not mix foods or drinks for the specific purpose of changing the color of one of the foods or beverages.
