No way to set a theme color to the default foreground color

`crossterm::style::Color` only supports the 8-bit ansi color codes, there is no way to make it emit code `39` which uses the default foreground color (which can be distinct from the normal and bright variants of both `white` and `black`).

As a workaround, adding support for parsing a string like `reset` to `Color::Reset` should give a similar result.

Search the color-handling code for uses of crossterm::style::Color and its string parsing. Start by tracing how colors are converted to terminal output, then support the default foreground behavior described by ANSI code 39 or the proposed reset input. Done means the CLI can select the terminal's default foreground color distinctly from white and black.

Written by the indexing model from the issue text.