Welcome.
and to save you some time...
But if I ask a question that has already been answered, I apologize in advance.
Depending on your OS and/or the program in question
1) Reboot
2) It's defined by the skin
3) 16 colors not 16 bit
4) Make sure you're using 32bit color
5) You need to be in builder mode, then right click on it
6) It's gotta be edited in the uifile
7) Renaming it won't work, you have to convert it
8) You can get more 'edge room' by placing your image within a larger blank .png.
9) Archive that version and try the beta
10) Reinstall SDC over itself