The candle contains an optical fibre alongside the wick which senses the light of the flame and activates the LED colour bulbs, green, red and blue to start changing colour. These primary colours mix together one-by-one to create all the colours of the rainbow e.g. red mixing with blue to make purple, green with blue making turquoise. To the eye, the candle appears to change colour by magic. When you blow out the candle, the colour changing will stop until the next time you light it.