Uh, usually it 'saves' it automatically. I mean my scratchpad has 2+ years of mixed colors, LOL.
I don't think this is something you can enable/disable, but I can go dig up some infos for you just
in case. If you have a ripped version of sai, that might be why it isn't functioning properly.
Okay, did a little digging. As long as the scratchpad is enabled and you don't clear it after you use it, anything
you paint in there should stay regardless of what image you're working on or if you save it or not, so it might
just be an issue with your sai itself. D:
I cleared mine, disabled then re-enabled it, painted some funky 5 color mess, closed sai, opened it again, all the colors
were still there.