8 bit png and all is fine, but you must know that there are 2 type of tileset, which include numbers to put in your script, the very last part
Type 0: Classic tileset type, like pics1.png
Type 1: Organized tileset, for modern servers like the one you want to make
For anything else,
THIS should help you
For the blank part uuhm... Try to upload it on your server, restart graal and it should be fine ?