The Custom Pan Burner utilizes only secondary air for combustion, that is, there is no air mixer that mixes air with the gas before ignition.   The burner relies solely on the air that is drawn into the flame to complete combustion. 

Blue flame indicates that a lot of air is being drawn into the flame.  A fireplace that draws very well will provide more air to the burner and result in a bluer flame.  Also, all of the gaps between the FireBalls dray air into the combustion.  To gain more yellow, you need to "choke" off the air at the burner between the FireBalls.  We recommend the following:

1) Place a layer of ember material on the sand.

2) Place the first layer of FireBalls on the embers.  Fill in the gaps between the balls with the ember material.   

3) Place the second layer of FireBalls and, again, fill in the gaps with ember material.  

4) Continue on this path until satisfied. 

 There is no other action that will yellow-up the flame other than to restrict the air available to the flame.