I've been working towards changing the PZF format used by ProSonic. There are a couple things about it that makes keeping it up to date really hard. I'm considering a slight format change that will make it much more similar to a file system on a computer. This will allow file sizes to be flexible, and it will make writing software to read files from the PZF archive easier.
This change came when I decided to design a file format to cycle through colors. After studying the original Sonic games, I came to the conclusion I would need to allow variable file sizes in order to make my engine fully compatible with the color cycling data from the original games.
I'm not sure if all the colors will be allowed to have cycle animations or if there will be a limit. I was thinking of limiting it to 32 colors, but maybe I can find a way to be more flexible there. Either way, 32 is far more than what was ever used in any level in the original Sonic games. The most colors being animated that I found in a single zone was 12. Since there are also under water animations (which would make it 24 colors being animated), ProSonic should therefore support at least 24, but more is better obviously.