Use $COLORFGBG to help decide whether to use a dark or light style

[crowsonkb]

Many terminals set $COLORFGBG to indicate the ANSI colors (or a best approximation) they are using as their foreground and background. For instance my iTerm2 sessions have it set to 0;15 (dark black on bright white) but in practice I have seen it set to 0;7, 7;0, and 15;0 by various terminal emulators. I propose looking at this variable to help decide which default style to use. is_light_bg starts off at None for unknown background color (note that this means we will still default to the dark style) and, if $COLORFGBG is present and parseable, becomes True or False.

If $PYPRETTYPRINTER_LIGHT_BACKGROUND is present it is allowed to override the detected setting based on $COLORFGBG.

[tommikaikkonen]

Thanks!