Summary for users:  Previously, there was one code context foreground and background font color setting, default or custom, on the extensions tab, that applied to all themes.  Now, each theme has it own setting, as with other color settings.  For builting themes, the foreground is the same as normal text; the background is a contrasting gray.  Context colors for custom themes are set on the Hightlights tab along with others.  When one starts IDLE from a console and loads a custom theme without definitions for 'context', one will see a warning message on the console.