My freehand mask is showing up black

Im sure this is something minor, but it has been a while since I have used combustion extensively. I am trying to get back into it, and for a project at work, I need the ability to mask out particles, to give the illusion of a trailing path of lava erupting from a volcano. I've drawn a mask, but when I go to the top of my branch, the mask is black. When I am at the mask level, everything looks exactly how I want. What could be causing this? Any help is greatly appreciated. Thanks in advance!