I have tried to balance the flash here in two fashions. One is to balance the amount of light so that the candle flame is still seen clearly. The other is that normally a flash has a day light temperature but that would look really blue here.

So I have used a CTO filter (full CTO) to change the flash temperature to around 3200 K instead of the usual 5600 K. This means that the colour temperature of the flash light is about the same as the color temperature on the light coming from the flame.