I just checked 33 official tilesets and they're all identical. Perhaps there is a switch in the level so that you can have night/day backgrounds or something.. Dunno.. perhaps it was never finished.. I just left it in because it IS stored twice in the BLOCKS file, so this way someone has the option to experiement if they so choose.

Also something to experiment re: backgrounds: look at the examples http://www.princeton.edu/~mspear/jj/ ... If you look closely the last color isn't part of the gradient (usually).. perhaps only 255 colors are used for the background and it's some kind of control for how vertically stretched the background is or if it wraps around
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or mirrors
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dunno.. I'm throwing out random ideas. I haven't played around with this stuff since pre-JCS94..

I *really* encourage anyone that figures anything out to share... but anyway..

I'll document everything I know and release the source sometimes in the near future. But for now, back to the university grind..