This is a trick which can be used for amusement or a change of pace rather than being a true show-piece.
The performer, who has been talking for quite a while, professes himself as becoming thirsty, so asks his assistant to bring in some wine so that they can have a quick sip. The assistant brings in a tray with a couple of bottles of wine and two glasses. One bottle is of red wine, one of white. He offers the assistant his choice and takes the other himself. When the bottles are opened and the wine poured, the red wine changes to white and the white becomes red! The performer and the assistant heap abuse on each other and the wine is removed from the set!
The red wine is prepared as follows: one gram of potassium permanganate with two grams of sulphuric acid dissolved in one quart of water; the glass into which it's poured contains a few drops of water saturated with sodium hyposulphite. The white wine is water with a considerable quantity of alcohol added: its glass contains a small pinch of aniline red.
THESE CHEMICALS ARE POISONOUS AND ON NO ACCOUNT MUST BE INGESTED. This is also why the assistant is involved rather than a member of the audience.
The bottles and the glasses must be removed quickly as in a few moments the contents will turn milky.
For best effect, the wine must come in bottles which appear to be real, with labels and properly sealed; they must also be of clear glass so that the colours obviously belong to the wine and not to the bottles. The trick can be done using decanters instead of bottles, of course, but the audience is bound to suspect chemical knavery anyway so it's better to make it seem less straightforward.