Color specifies the color to use when displaying the overstrike. It may have any of the forms accepted by Tk_GetColor. If color has not been specified, or if it is specified as an empty string, then the color specified by the -foreground tag option is used.
This option is deprecated, option -overstrikecolor should be used. It will be supported only for compatibility reasons, but may be removed in a future release.
Color specifies the color to use when displaying the underline. It may have any of the forms accepted by Tk_GetColor. If color has not been specified, or if it is specified as an empty string, then the color specified by the -foreground tag option is used.
This option is deprecated, option -underlinecolor should be used. It will be supported only for compatibility reasons, but may be removed in a future release.
The names of the relatively new options -overstrikefg and -underlinefg are unsuccessful:
It's the color of the overstrike, thus: -overstrikecolor.
An overstrike has no background, it's clear that -overstrikecolor is denoting the foreground color.
This conforms better with the naming standard of older tag options, one example is -lmargincolor. This attribute is not named -lmarginbackground, nor is it named -lmarginbg.
Moreover it's not standard to use tokens like fg and bg, except for additional abbreviations. The widget option -highlightbackground is named highlightbackground, and not highlightbg.