My stone is light grey in colour and will not light. What is wrong?

Fragrance is not being delivered to the stone. Check that your Lamp contains Lamp Fragrance, this is especially important with opaque lamps. Check also that the wick is inserted fully into the Lamp so that the bottom of the wick is in the fragrance. After checking this, put the snuffer-cap on the Lamp for 20-30 minutes to prime it and then re-light.