Suggestion: Consider changing default color from ColorWhite to ColorClear

Right now, when working with light terminal background, there are quite a few places that need to be overridden from `ColorWhite` to `ColorClear` (or some other color that is readable on white background).

Not only this makes development and experimentation a little lengthier, I suspect it also causes developers who publish packages that rely on termui to have a default theme that is not friendly to light background users.

I believe that if `ColorClear` is used as the default color, and both `ColorBlack` and `ColorWhite` are avoided in all the defaults, this will be a good starting point for everybody, and will provide a sensible theme that works out of the box for both dark and light background users.

The issue does not name specific files, tests, or entry points. Start by locating termui's default color definitions and reviewing where ColorWhite, ColorBlack, and ColorClear are used in defaults. Done means defaults avoid hard-coded black and white where appropriate and provide readable behavior on both light and dark terminal backgrounds.

Written by the indexing model from the issue text.