Tzove’a is a melakha with the objective of making something more beautiful. In the Mishkan, the woolen threads of the curtains were dyed indigo, royal purple, and scarlet. Even though the melakha of Kotev can be described as “dyeing” a page with letters, there is a difference between Kotev and Tzove’a. The goal of writing is to express an idea. Even when the “writing” is a picture of a house or a tree, the goal is still to express an idea, and that is how one transgresses Kotev. In contrast, the goal of dyeing is not to express an idea, but to beautify an item. Therefore, one who creates a meaningful image on paper or on a wall transgresses Kotev, and if he then colors it to beautify it he transgresses Tzove’a (y. Shabbat 7:2).
Therefore, it is prohibited by Torah law to paint, color, or dye walls, cabinets, utensils, fabric, or clothing on Shabbat. The specific color is irrelevant; any color that beautifies is prohibited by Torah law. Even if the paint is colorless and merely adds glaze or shine, it is prohibited, because shine is considered color. It is prohibited by Torah law to paint a wall even if it was previously painted with the same or a different color.
It is also prohibited by Torah law to polish shoes. Even if the polish is neutral or colorless, it is prohibited by Torah law, because it makes the shoes shine. If the polish is a cream that is spread on the shoes, then one who applies it also transgresses Memare’aĥ (section 6 below). If the polish improves the leather, then one transgresses Me’abed as well (MB 327:12, 16; see section 6 below). Even if the polish was applied before Shabbat, one may not buff the shoes on Shabbat to make them shine, because shine is considered color. However, if there is dust on the shoes, one may gently remove it with a rag (SSK 15:40).
The Torah prohibition of Tzove’a is limited to permanent dyes. If the color will come off by itself within a short time, the prohibition is rabbinic (MT 9:13).
If one’s hands become stained with fruit, blood, or any other substance, le-khatĥila he should first wash his hands and only afterward dry them with a towel, to avoid “dyeing” the towel. Similarly, if juice spills on a tablecloth, the one who wipes it off should be careful not to drag the juice along the cloth as that will dye the tablecloth. Even though such “dyeing” dirties the tablecloth rather than beautifying it, those who are stringent maintain that since it is normal to dye such a cloth, it is rabbinically prohibited (SA 320:20). In times of need one may be lenient, since many poskim say that adding color in a way that dirties the object is not prohibited (MB 320:59; Kaf Ha-ĥayim ad loc. 122).
Since bandages or tissues are not normally dyed, they may be used to clean up blood or other colored substances. Since the color added dirties material that is not normally dyed, there is no prohibition (SAH §302, Kuntres Aĥaron).
Everyone agrees that there is no issue of staining the hands or mouth when eating strawberries or other brightly colored foods, because this is not the normal way to color skin, and any such coloring is actually dirtying the skin (MB 320:58). However, one may not put on makeup, as we explained earlier (14:4).
If a toilet has an automatic toilet bowl cleaner that colors the water with every flush, poskim disagree whether one may flush the toilet on Shabbat. Some maintain that since people are interested in the water being colored, it is rabbinically prohibited even though the color is present only briefly. Others maintain that since the primary goal is to clean the toilet, and the color is just incidental, one may flush the toilet. In practice, it is preferable to use a clear toilet bowl cleaner. However, if one finds himself in a place where the cleaning material is colored, he may flush the toilet. Those who wish to be lenient and use a colored toilet bowl cleaner have an opinion to rely upon.