Sometimes if I type in an extra 0, GrowFX does its thing, and my memory modules nearly burst out of their sockets. I usually have to reboot. To alleviate this, I suggest adding a path/knot limit and a triangle limit. If this limit is reached on build, GrowFX stops building, shows a message and switches to manual mode.
Secondly, when tweaking vertex colours, the tree graph shouldn't have to rebuild.Perhaps the vertices should have internal attributes (per element, length along path) that the vertex colours can derive from rather than rebuilding the mesh to bake those values in?