Hal, I have seen this effect quite often over the past year; it is quite common in some Julia Set zooms, when you zoom into the black lake multicolored horizontal lines appear and finally the lake is filled with color. This can be seen in some of my animations, such as Eye Of Hell #2 and Triskaidekaphobia, and especially "Star Gate", which is no longer on my site (I can put it back up if anyone wants to see it). I also noticed it with some of the "multifractals" and other "unusual" fractals I have been playing with. Up till now I assumed it was a normal, if not understood, fractal phenomenon, and I have been pulling my hair out trying to figure it out. In animation sequences, it looks not unlike a "bifurcation" effect. Actually, I think the effect looks rather cool, especially with zoom animations. It never occured to me that it could be a "bug", or due to a fractint version, or a parameter tweak, as Lee suggested. I still don't know that it is. I will try Lee suggestions; I have not played much with periodicity setting, so I can tell you nothing about that. However, lowering the iteration count will often generate a fractal that looks completely different. BTW, I made an animation on a variation of the "Julia Rectangle" image, it is called Bad Trip and it is now on my site. Stay Amazed! JoTz