Candles are a classic when it comes to spells. Candles are often used in spells to represent something that you would like as the outcome of a spell. For example, when it comes to meditation, white candles are popular as white is a colour that is associated with peace. Blue may also be picked for it's association with calm and peace. If the meditation is supposed to be for preperation rather than relaxing, one might chose silver, as it can represent spirituality and intuition.
As you can see, candles can have a lot of meaning, as well as importance through those meanings. But it isn't just the colour that may be considered as important. The burning time, and maybe even the size/shape, of the candle can be important too. Even outside of spell-casting and meditation. One may find oneself wanting a large rabbit-shapped candle purely as a decorational piece. Or one may want a long-lasting candle to get one's money's worth. Whereas a witch may want himself a tea-light that burns quickly for a spell that would usually require patience. Or a meditator may find herself wanting a more slow-burning candle that will last the duration of her YouTube playlist.
Picking a candle that is perfect for your purpose may seem hard or confusing... Or it may seem incredibly silly. Whichever the case, if in doubt, white shall suffice. It makes a great substitute colour, being the perfect blank slate, and shouldn't clash with the colours in one's environment. However, if you would rather have a candle more specific to your needs, then this book is for you.