In ST2 I use a customized version of Slush & Poppies, but in ST3 it gives a cryptic “Bad XML” error. In fact this happens even if I take the Slush & Poppies from /opt/sublime_text/Packages/Color Scheme - Default.sublime-package, copy it to ~/.config/sublime-text-3/my.tmTheme, put in the appropriate “color_scheme”: … line in my preferences file and save.
Has anyone else experienced this problem?