Candles come in many colours, and the colours can have many meanings. Colours are known to represent things in their own right, such as wearing them in clothes and accessories, or having walls painted a certain colour. Colours can have a psychological affect, as our brains associate certain colours with certain emotions. For example, lilac is a colour that makes us relax. Lilac is my favourite colour, and I try to make sure that I can have lilac with me at all times. It makes me happy and keeps me calm, bringing a feeling of comfort.
You can carry colours with you to encourage positive traits that you desire to see in yourself. For example, if you want good luck, wearing green may be useful. Or if you want to encourage happiness, you could try wearing gold. You can also just try wearing your favourite colour to lift your mood, since your favourite colour should give you a feeling of happiness and comfort.
In this book, I will be talking about colours in reference to candles and spellcasting, but if you would like to know more about colours and their meanings generally, you should search for colour symbolism.