I assume you're planning to actually build this into a graphics set, rather than just create images, right? And if so, given that you're sticking to the 8-color limit, I also assume you're planning to make it for DOS/Lemmix by using LemSet (I don't think any other tools to compile it exist yet)?
I'll have to point out that you're doing a few things wrong:
- Your filenames. These should be either (style name)_t##.bmp / (style name)_o##.bmp or just plain t##.bmp / o##.bmp. You've named them cake0.bmp, cake1.bmp, etc for terrain - they should be either cake_t00.bmp, cake_t01.bmp, etc or just t00.bmp, t01.bmp, etc. Objects likewise, you've named them with descriptive names, but they should be either cake_o00.bmp etc or just o00.bmp etc. (In all official styles and the LPII styles, the exit is o00 and the window is o01. The window being o01 is a requirement - o01 must be a window, and windows must be o01 - but the exit being o00 is NOT a requirement, o00 can be anything you want and the exit can be in any slot you want.)
- The window. The first frame should be with the window fully open, the SECOND frame should be the fully closed one (from there, the remaining frames are the opening sequence). If you look how a Lemmini GIF file of a window is laid out, LemSet expects the same thing except with the last frame moved to the first position (this may seem weird, but this is in fact how it's stored in the graphic set files).
- This is more a precaution than something I noticed with your files, but keep in mind that a lemming checks for trigger areas one pixel below its feet, not in line with its feet. I attached two images to illustrate this. In both, the red dot represents the "normal" check position for the lemming - this position is used for almost all checks for both terrain and trigger areas. In the first picture, as you can see, the lemming is checking one pixel lower than the trigger area, and thus would not trigger anything. In the second, it would trigger the area. (The only things that are ever checked for in any other position are one-way arrows, steel areas and terrain; it should be fairly obvious when these other checks are but if you want more info just ask.)
- Don't forget you need an INI file describing the style (though you mention that's not done yet). I also find it far easier to work with a pallete.bmp rather than pallete entries in the INI.