There aren't specific NTSC or PAL modes to select in this release. I found a thread on Atari Age which talked about possibly being able to force it in the future. Instead, I did find some of the cartridges I was playing in the stella.pro file and put the "Display.Format" value of "NTSC" (which was missing for all of them, whereas there are a lot of PAL ones) and this didn't change anything.
Colors are still yuck. I guess I'll just keep an eye out for the next release.