Red and black pillars, or double-action candles, are used in workings to make two conditions happen at the same time. Red is generally seen as a color of attraction, and black: a color of chaos. Used often in reversal workings to cast off crossing, slander, or evil eye, and return it back to the sender, then allow the positive conditions to return to you. 
One way to work these candles is to dress the black portion of the candle in Reversal Oil, and the red portion in whatever condition you desire: Come to Me Love Oil for new love, Crown of Success Oil for success in all endeavours, and Money Drawing Oil for wealth, or any other. Expose the wick at the bottom of the candle, and with a candle holder, burn both ends of the candle at the same time.
Read More Reversal Spells & Workings Here.