Flood Fill is an amazing feature, but one thing that's a bit of a headache is that it requires black pixel boundaries to work, and the edge detect by design has to be at least 2 pixels thick. This creates some undesirable results unless you're working at resolutions high enough that the black lines will dissapear when you resize.
In this specific case, each cell from the Cell noise node already contains a boundary. If Flood Fill could be calculated without the edge detect, it would be possible to eliminate the black lines, correct?
Seems like something like this would give really nice results at lower resolutions: