Basically, when it comes to candle magic, it doesn't matter what shape or color the candle you're working with is. The candle serves to bundle energies and elemental powers and to carry out the magic in a concentrated manner. However, the conscious use of colors can be very helpful in visualization, because colors have their very own vibration and effect on our subconscious. With the right color, your magic may be easier and more effective.
I use the candle colors as follows:
🤍White - clarity, purification, new beginnings
🖤Black - Protection, Ban, Repel
❤️Red - Love, passions, lust, powerful Mars energy
💖Pink - love, friendship, self-love, harmony
💙Blue - peace, harmony, balance, feelings
💚Green - luck, success, money, health
💛Yellow - solar power, vitality, communication
🧡Orange - strength, assertiveness, creativity
💜Purple - Third eye, spirituality, magical powers, subconscious
Each magical practitioner may feel these associations a little differently, so there is plenty of leeway here. If you're not sure which color is right, trust your gut feeling. Ultimately, it's about your own personal magic being successful - so choose the color that intuitively appeals to you. And when in doubt, white is always okay.